Fix warnings.

Author: qwandor

generate-sysregs/src/main.rs

@@ -78,15 +78,15 @@ impl RegisterBit {
                 trace!("  Reserved field: {:?}", field.rangeset);
                 None
             }
-            FieldEntry::ImplementationDefined(implementation_defined_field) => todo!(),
+            FieldEntry::ImplementationDefined(_implementation_defined_field) => todo!(),
             FieldEntry::ConditionalField(field) => {
                 trace!(
                     "  Conditional field: {:?}, {:?}",
                     field.name, field.rangeset
                 );
                 Self::from_conditional_field(field)
             }
-            FieldEntry::ConstantField(constant_field) => todo!(),
+            FieldEntry::ConstantField(_constant_field) => todo!(),
         }
     }