lib: fix safety comment missing space

While merging the pin-init PR for v6.17 I noticed this typo, thus fix
it upstream.

Fixes: fdd6bcb ("add `zeroed()` & `Zeroable::zeroed()` functions")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

src/lib.rs

@@ -1592,7 +1592,7 @@ pub fn init_zeroed<T: Zeroable>() -> impl Init<T> {
 /// assert_eq!(point.y, 0);
 /// ```
 pub const fn zeroed<T: Zeroable>() -> T {
-    // SAFETY:By the type invariants of `Zeroable`, all zeroes is a valid bit pattern for `T`.
+    // SAFETY: By the type invariants of `Zeroable`, all zeroes is a valid bit pattern for `T`.
     unsafe { core::mem::zeroed() }
 }