ext2: Annotate implicit fall through in __ext2_truncate_blocks

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

This commit removes the following warnings:

  fs/ext2/inode.c:1237:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
  fs/ext2/inode.c:1244:7: warning: this statement may fall through [-Wimplicit-fallthrough=]

Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext2/inode.c

@@ -1239,6 +1239,7 @@ do_indirects:
 				mark_inode_dirty(inode);
 				ext2_free_branches(inode, &nr, &nr+1, 1);
 			}
+			/* fall through */
 		case EXT2_IND_BLOCK:
 			nr = i_data[EXT2_DIND_BLOCK];
 			if (nr) {
@@ -1246,6 +1247,7 @@ do_indirects:
 				mark_inode_dirty(inode);
 				ext2_free_branches(inode, &nr, &nr+1, 2);
 			}
+			/* fall through */
 		case EXT2_DIND_BLOCK:
 			nr = i_data[EXT2_TIND_BLOCK];
 			if (nr) {