fsnotify: remove redundant parameter judgment

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

Link: https://lore.kernel.org/r/20220311151240.62045-1-libang.linuxer@gmail.com
Signed-off-by: Bang Li <libang.linuxer@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>