fatfs: remove redundant judgment

iput() has already judged the incoming parameter, so there is no need to
repeat outside.

Link: https://lkml.kernel.org/r/1648265418-76563-1-git-send-email-fengyubo3@huawei.com


Signed-off-by: Yubo Feng <fengyubo3@huawei.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>