NAME
    CloseDevice - terminate access to the audio device

SYNOPSIS
    CloseDevice(iORequest);
                    A1

FUNCTION
    The CloseDevice routine notifies the audio device that it will no
    longer be used.  It takes an I/O audio request block (IOAudio) and
    clears the device pointer (io_Device).  If there are any channels
    allocated with the same allocation key (ioa_AllocKey), CloseDevice
    frees (ADCMD_FREE) them. CloseDevice decrements the open count, and if
    it falls to zero and an expunge (Expunge) is pending, the device is
    expunged.

INPUTS
    iORequest   - pointer to audio request block (struct IOAudio)
            io_Device   - pointer to device node, must be set by (or
                          copied from I/O block set by) open (OpenDevice)
            io_Unit     - bit map of channels to free (ADCMD_FREE) (bits 0
                          thru 3 correspond to channels 0 thru 3)
            ioa_AllocKey- allocation key, used to free channels

OUTPUTS
    iORequest - pointer to audio request block (struct IOAudio)
            io_Device   - set to -1
            io_Unit     - set to zero