staging: comedi: rtd520: Prefer using macro DIV_ROUND_UP

The macro DIV_ROUND_UP performs the computation
(((n) + (d) - 1) /(d)). It clarifies the divisor calculations.
This was done using the coccinelle script:
@@
expression e1;
expression e2;
@@
(
- ((e1) + e2 - 1) / (e2)
+ DIV_ROUND_UP(e1,e2)
|
- ((e1) + (e2 - 1)) / (e2)
+ DIV_ROUND_UP(e1,e2)
)

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/rtd520.c

@@ -892,9 +892,8 @@ static int rtd_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 				devpriv->xfer_count = cmd->chanlist_len;
 			} else {	/* make a multiple of scan length */
 				devpriv->xfer_count =
-				    (devpriv->xfer_count +
-				     cmd->chanlist_len - 1)
-				    / cmd->chanlist_len;
+				    DIV_ROUND_UP(devpriv->xfer_count,
+						 cmd->chanlist_len);
 				devpriv->xfer_count *= cmd->chanlist_len;
 			}
 			devpriv->flags |= SEND_EOS;