staging: comedi: ii_pci20kc: use comedi_offset_munge()

For aesthetics, use the helper function to handle the munging of the
analog output data from offset binary to 2's complement and the analog
input data from 2's complement to offset binary.
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/ii_pci20kc.c

@@ -153,9 +153,8 @@ static int ii20k_ao_insn_write(struct comedi_device *dev,
 
 		s->readback[chan] = val;
 
-		/* munge data */
-		val += ((s->maxdata + 1) >> 1);
-		val &= s->maxdata;
+		/* munge the offset binary data to 2's complement */
+		val = comedi_offset_munge(s, val);
 
 		writeb(val & 0xff, iobase + II20K_AO_LSB_REG(chan));
 		writeb((val >> 8) & 0xff, iobase + II20K_AO_MSB_REG(chan));
@@ -243,11 +242,8 @@ static int ii20k_ai_insn_read(struct comedi_device *dev,
 		val = readb(iobase + II20K_AI_LSB_REG);
 		val |= (readb(iobase + II20K_AI_MSB_REG) << 8);
 
-		/* munge two's complement data */
-		val += ((s->maxdata + 1) >> 1);
-		val &= s->maxdata;
-
-		data[i] = val;
+		/* munge the 2's complement data to offset binary */
+		data[i] = comedi_offset_munge(s, val);
 	}
 
 	return insn->n;