staging: comedi: das1800: use sample manipulation helpers

Use the recently added sample manipulation helpers to remove the hardcoded
assumption of the sample size.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: NIan Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/das1800.c

@@ -535,7 +535,7 @@ static void das1800_flush_dma_channel(struct comedi_device *dev,
 
 	/*  figure out how many points to read */
 	num_bytes = devpriv->dma_transfer_size - get_dma_residue(channel);
-	num_samples = num_bytes / sizeof(short);
+	num_samples = comedi_bytes_to_samples(s, num_bytes);
 
 	/* if we only need some of the points */
 	if (cmd->stop_src == TRIG_COUNT && devpriv->count < num_samples)