staging: comedi: cb_das16_cs: fix ai mux register programming

The ai mux register is used program the hi/lo channels in a scan.
According to the user manual, the hi and lo channels should be
the same  to sample one channel.

Introduce some macros to set the appropriate bits in the ai mux
register and fix the ai (*insn_read).
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/cb_das16_cs.c

@@ -46,6 +46,10 @@
  */
 #define DAS16CS_AI_DATA_REG		0x00
 #define DAS16CS_AI_MUX_REG		0x02
+#define DAS16CS_AI_MUX_HI_CHAN(x)	(((x) & 0xf) << 4)
+#define DAS16CS_AI_MUX_LO_CHAN(x)	(((x) & 0xf) << 0)
+#define DAS16CS_AI_MUX_SINGLE_CHAN(x)	(DAS16CS_AI_MUX_HI_CHAN(x) |	\
+					 DAS16CS_AI_MUX_LO_CHAN(x))
 #define DAS16CS_MISC1_REG		0x04
 #define DAS16CS_MISC2_REG		0x06
 #define DAS16CS_TIMER_BASE		0x08
@@ -111,7 +115,8 @@ static int das16cs_ai_rinsn(struct comedi_device *dev,
 	int ret;
 	int i;
 
-	outw(chan, dev->iobase + DAS16CS_AI_MUX_REG);
+	outw(DAS16CS_AI_MUX_SINGLE_CHAN(chan),
+	     dev->iobase + DAS16CS_AI_MUX_REG);
 
 	devpriv->status1 &= ~0xf320;
 	devpriv->status1 |= (aref == AREF_DIFF) ? 0 : 0x0020;