staging: comedi: daqboard2000: support 4 AO channels

The driver supports DaqBoard/2000 and DaqBoard/2001. DaqBoard/2000 has 2
AO channels, but DaqBoard/2001 has 4 AO channels.  The driver currently
only supports 2 AO channels, but supporting 4 channels is just a case of
setting the `n_chan` member of the COMEDI subdevice to 4 instead of 2.

Add a new boolean flag member `has_2_ao` to `struct db2k_boardtype` to
be set to `true` if the board only has 2 AO channels.  Set this to
`true` in the element of `db2k_boardtypes[]` that corresponds to the
DaqBoard/2000.  Use it in `db2k_auto_attach()` to initialize the number
of AO channels to 2 or 4, as appropriate.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/daqboard2000.c

@@ -114,7 +114,7 @@
 #define DB2K_FIRMWARE		"daqboard2000_firmware.bin"
 
 #define DB2K_SUBSYSTEM_IDS2	0x0002	/* Daqboard/2000 - 2 Dacs */
-#define DB2K_SUBSYSTEM_IDS4	0x0004	/* Daqboard/2000 - 4 Dacs */
+#define DB2K_SUBSYSTEM_IDS4	0x0004	/* Daqboard/2001 - 4 Dacs */
 
 static const struct comedi_lrange db2k_ai_range = {
 	13, {
@@ -248,12 +248,14 @@ static const struct comedi_lrange db2k_ai_range = {
 struct db2k_boardtype {
 	const char *name;
 	int id;
+	bool has_2_ao:1;	/* false: 4 AO chans; true: 2 AO chans */
 };
 
 static const struct db2k_boardtype db2k_boardtypes[] = {
 	{
 		.name		= "ids2",
 		.id		= DB2K_SUBSYSTEM_IDS2,
+		.has_2_ao	= true,
 	},
 	{
 		.name		= "ids4",
@@ -758,7 +760,7 @@ static int db2k_auto_attach(struct comedi_device *dev,
 	/* ao subdevice */
 	s->type = COMEDI_SUBD_AO;
 	s->subdev_flags = SDF_WRITABLE;
-	s->n_chan = 2;
+	s->n_chan = board->has_2_ao ? 2 : 4;
 	s->maxdata = 0xffff;
 	s->insn_write = db2k_ao_insn_write;
 	s->range_table = &range_bipolar10;