f2fs: fix to report error number of f2fs_find_entry

This patch fixes to report the right error number of f2fs_find_entry to
its caller.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

 Conflicts:
	fs/f2fs/namei.c