staging: comedi: ni_labpc: tidy up labpc_ai_scan_mode()

This function checks the cmd->chanlist to determine the scan mode
used to sample the analog inputs. All possible modes are checked
so the final pr_err() and return 0 can never be reached.

Tidy up the function a bit and remove the unreachable code.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_labpc.c

@@ -531,24 +531,26 @@ static void labpc_adc_timing(struct comedi_device *dev, struct comedi_cmd *cmd,
 
 static enum scan_mode labpc_ai_scan_mode(const struct comedi_cmd *cmd)
 {
+	unsigned int chan0;
+	unsigned int chan1;
+
 	if (cmd->chanlist_len == 1)
 		return MODE_SINGLE_CHAN;
 
-	/* chanlist may be NULL during cmdtest. */
+	/* chanlist may be NULL during cmdtest */
 	if (cmd->chanlist == NULL)
 		return MODE_MULT_CHAN_UP;
 
-	if (CR_CHAN(cmd->chanlist[0]) == CR_CHAN(cmd->chanlist[1]))
-		return MODE_SINGLE_CHAN_INTERVAL;
+	chan0 = CR_CHAN(cmd->chanlist[0]);
+	chan1 = CR_CHAN(cmd->chanlist[1]);
 
-	if (CR_CHAN(cmd->chanlist[0]) < CR_CHAN(cmd->chanlist[1]))
+	if (chan0 < chan1)
 		return MODE_MULT_CHAN_UP;
 
-	if (CR_CHAN(cmd->chanlist[0]) > CR_CHAN(cmd->chanlist[1]))
+	if (chan0 > chan1)
 		return MODE_MULT_CHAN_DOWN;
 
-	pr_err("ni_labpc: bug! cannot determine AI scan mode\n");
-	return 0;
+	return MODE_SINGLE_CHAN_INTERVAL;
 }
 
 static int labpc_ai_check_chanlist(struct comedi_device *dev,