f2fs: remove extra inode_unlock() in error path

This commit removes an extra inode_unlock() that is being done in function
f2fs_ioc_setflags error path.  While there, get rid of a useless 'out'
label as well.

Fixes: 0abd675e97e6 ("f2fs: support plain user/group quota")
Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>