staging: comedi: ni_mio_common: use CR_CHAN more consistently

Generally, the CR_CHAN macro is/should be used to access the relevant bits
for channel identification in cmd->*_arg when the corresponding
cmd->*_src==TRIG_EXT, including cmd->convert_arg in this case.

This patch does not fix a bug per se, as NISTC_AI_MODE1_CONVERT_SRC() already
masks the value sufficiently, but using CR_CHAN() here makes the code clearer as
it avoids passing some irrelevant bits to NISTC_AI_MODE1_CONVERT_SRC() in the
first place.
Signed-off-by: Spencer E. Olson <olsonse@umich.edu>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_mio_common.c

@@ -2428,7 +2428,8 @@ static int ni_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 		ni_stc_writew(dev, mode2, NISTC_AI_MODE2_REG);
 		break;
 	case TRIG_EXT:
-		mode1 |= NISTC_AI_MODE1_CONVERT_SRC(1 + cmd->convert_arg);
+		mode1 |= NISTC_AI_MODE1_CONVERT_SRC(1 +
+						    CR_CHAN(cmd->convert_arg));
 		if ((cmd->convert_arg & CR_INVERT) == 0)
 			mode1 |= NISTC_AI_MODE1_CONVERT_POLARITY;
 		ni_stc_writew(dev, mode1, NISTC_AI_MODE1_REG);