ext4: fix setup_new_group_blocks locking

setup_new_group_blocks() manipulates the group descriptor block bh
under the block_bitmap bh's lock.  It shouldn't matter since nobody
but resize should be touching these blocks, but it's worth fixing up.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>

fs/ext4/resize.c

@@ -199,10 +199,10 @@ static int setup_new_group_blocks(struct super_block *sb,
 			brelse(gdb);
 			goto exit_bh;
 		}
-		lock_buffer(bh);
-		memcpy(gdb->b_data, sbi->s_group_desc[i]->b_data, bh->b_size);
+		lock_buffer(gdb);
+		memcpy(gdb->b_data, sbi->s_group_desc[i]->b_data, gdb->b_size);
 		set_buffer_uptodate(gdb);
-		unlock_buffer(bh);
+		unlock_buffer(gdb);
 		ext4_journal_dirty_metadata(handle, gdb);
 		ext4_set_bit(bit, bh->b_data);
 		brelse(gdb);