staging: comedi: drivers: Use DIV_ROUND_CLOSEST

The kernel.h macro DIV_ROUND_CLOSEST performs the computation
`(x +d/2)/d` but is perhaps more readable.

The Coccinelle script used is as follows:
// <smpl>
@@
expression x,__divisor;
@@
- (((x) + ((__divisor) / 2)) / (__divisor))
+ DIV_ROUND_CLOSEST(x,__divisor)
// </smpl>

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>