filesystems-minfs: mark superblock buffer head as dirty

[Bingqiang-Jing]

I think there is just update sbi (struct minfs_sb_info) but not sbi->sbh (struct minfs_super_block).

kernel/minfs.c:332

	/* TODO 7/2: Mark the inode as used in the bitmap and mark
	 * the superblock buffer head as dirty.
	 */
	__test_and_set_bit(idx, &sbi->imap);
	mark_buffer_dirty(sbi->sbh);

       
       /********* fix like this ? ********/
       __test_and_set_bit(idx, &sbi->imap);

       /* update sbi->sbh */
       struct minfs_super_block *ms;
       ms = (struct minfs_super_block *)(sbi->sbh->b_data);
       ms->imap = sbi->imap;

       mark_buffer_dirty(sbi->sbh);