Update the docstrings to match the actual code defaults (#8701)

Fixes #8689

### Description

Update the docstrings to match the actual code defaults.

1. AsymmetricFocalLoss (line 103, 111): `gamma`
2. AsymmetricUnifiedFocalLoss (line 162, 171): `gamma`
3. AsymmetricUnifiedFocalLoss (line 172): `epsilon`

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [ ] New tests added to cover the changes.
- [ ] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [ ] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [ ] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

---------

Signed-off-by: ytl0623 <david89062388@gmail.com>
Signed-off-by: Eric Kerfoot <17726042+ericspod@users.noreply.github.com>
Co-authored-by: Eric Kerfoot <17726042+ericspod@users.noreply.github.com>

Author: ytl0623

monai/losses/unified_focal_loss.py

@@ -44,7 +44,7 @@ def __init__(
         Args:
             to_onehot_y: whether to convert `y` into the one-hot format. Defaults to False.
             delta : weight of the background. Defaults to 0.7.
-            gamma : value of the exponent gamma in the definition of the Focal loss  . Defaults to 0.75.
+            gamma : value of the exponent gamma in the definition of the Focal loss. Defaults to 0.75.
             epsilon : it defines a very small number each time. similarly smooth value. Defaults to 1e-7.
         """
         super().__init__(reduction=LossReduction(reduction).value)
@@ -108,7 +108,7 @@ def __init__(
         Args:
             to_onehot_y : whether to convert `y` into the one-hot format. Defaults to False.
             delta : weight of the background. Defaults to 0.7.
-            gamma : value of the exponent gamma in the definition of the Focal loss  . Defaults to 0.75.
+            gamma : value of the exponent gamma in the definition of the Focal loss. Defaults to 2.
             epsilon : it defines a very small number each time. similarly smooth value. Defaults to 1e-7.
         """
         super().__init__(reduction=LossReduction(reduction).value)
@@ -167,10 +167,11 @@ def __init__(
         Args:
             to_onehot_y : whether to convert `y` into the one-hot format. Defaults to False.
             num_classes : number of classes, it only supports 2 now. Defaults to 2.
+            weight : weight for each loss function. Defaults to 0.5.
+            gamma : value of the exponent gamma in the definition of the Focal loss. Defaults to 0.5.
             delta : weight of the background. Defaults to 0.7.
-            gamma : value of the exponent gamma in the definition of the Focal loss. Defaults to 0.75.
-            epsilon : it defines a very small number each time. similarly smooth value. Defaults to 1e-7.
-            weight : weight for each loss function, if it's none it's 0.5. Defaults to None.
+
+
 
         Example:
             >>> import torch