fs: clean up after mandatory file locking support removal

Commit 3efee0567b4a ("fs: remove mandatory file locking support") removes
some operations in functions rw_verify_area().

As these functions are now simplified, do some syntactic clean-up as
follow-up to the removal as well, which was pointed out by compiler
warnings and static analysis.

No functional change.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>