f2fs: remove redundant parameter judgment

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

Signed-off-by: Wang Xiaojun <wangxiaojun11@huawei.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>