f2fs: fix to return 0 if err == -ENOENT in f2fs_readdir

Commit 57b62d29 ("f2fs: fix to report
error in f2fs_readdir") causes f2fs_readdir to return -ENOENT when
get_lock_data_page returns -ENOENT. However, the original logic is to
continue when get_lock_data_page returns -ENOENT, but it forgets to
reset err to 0.

This will cause getdents64 incorretly return -ENOENT when lastdirent is
NULL in getdents64. This will lead to a wrong return value for syscall
caller.
Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/dir.c

@@ -888,6 +888,7 @@ static int f2fs_readdir(struct file *file, struct dir_context *ctx)
 		kunmap(dentry_page);
 		f2fs_put_page(dentry_page, 1);
 	}
+	err = 0;
 out:
 	fscrypt_fname_free_buffer(&fstr);
 	return err;