staging: comedi: me4000: fix aref test in ai_write_chanlist()

The 'aref' (CR_AREF) values are all AREF_* defines. The SDF_* defines are
subdevice flags. Fix the test in this function.

Reported by: coverity
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/me4000.c

@@ -731,7 +731,7 @@ static int ai_write_chanlist(struct comedi_device *dev,
 		else
 			entry |= ME4000_AI_LIST_RANGE_BIPOLAR_10;
 
-		if (aref == SDF_DIFF)
+		if (aref == AREF_DIFF)
 			entry |= ME4000_AI_LIST_INPUT_DIFFERENTIAL;
 		else
 			entry |= ME4000_AI_LIST_INPUT_SINGLE_ENDED;