Translate rba to aba

        Entry:
          AX = 1C0Eh
          CH = low 8 bits of cylinder number
          CL = sector number, high two bits of cylinder number in bits 6 and 7
          DH = head number
          DL = drive number
          ES:BX -> ABA number

        Return:
          CF set on error
            AH = status

        Note:   ABA (absolute block address) format can be found in IBM
                ESDI Adapter Technical Reference by using it's Device
                Configuration Status Block