ext4: annotate implicit fall throughs

There is a plan to build the kernel with -Wimplicit-fallthrough and
these places in the code produced warnings (W=1). Fix them up.

This commit remove the following warnings:

  fs/ext4/hash.c:233:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
  fs/ext4/hash.c:246:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>

fs/ext4/hash.c

@@ -231,6 +231,7 @@ int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
 		break;
 	case DX_HASH_HALF_MD4_UNSIGNED:
 		str2hashbuf = str2hashbuf_unsigned;
+		/* fall through */
 	case DX_HASH_HALF_MD4:
 		p = name;
 		while (len > 0) {
@@ -244,6 +245,7 @@ int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
 		break;
 	case DX_HASH_TEA_UNSIGNED:
 		str2hashbuf = str2hashbuf_unsigned;
+		/* fall through */
 	case DX_HASH_TEA:
 		p = name;
 		while (len > 0) {