Verify Sectors

Entry:
    AH = 44h
    DL = Drive number
    DS:SI = Disk address packet
Exit:
    carry clear
        AH = 0
    carry set
        AH = error code

This function verifies blocks without transferring data between disk and system memory.

In the event of an error, the block_count field of the disk address packet is filled in with the number of blocks verified before the error occurred.