INT 21 - DOS 2+ - IOCTL - WRITE TO BLOCK DEVICE CONTROL CHANNEL

	AX = 4405h
	BL = drive number (00h = default, 01h = A:, etc)
	CX = number of bytes to write
	DS:DX -> data to write
Return: CF clear if successful
	    AX = number of bytes actually written
	CF set on error
	    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)
Notes:	format of data is driver-specific
	this function was not supported by Digital Research's DOS Plus
SeeAlso: AX=4403h"DOS",AX=4404h"DOS",INT 2F/AX=122Bh