f2fs: introduce dot and dotdot name check

This patch adds an inline function to check dot and dotdot names.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/hash.c b/fs/f2fs/hash.c
index a844fcf..71b7206 100644
--- a/fs/f2fs/hash.c
+++ b/fs/f2fs/hash.c
@@ -79,8 +79,7 @@
 	const unsigned char *name = name_info->name;
 	size_t len = name_info->len;
 
-	if ((len <= 2) && (name[0] == '.') &&
-		(name[1] == '.' || name[1] == '\0'))
+	if (is_dot_dotdot(name_info))
 		return 0;
 
 	/* Initialize the default seed for the hash checksum functions */