staging: comedi: adq12b: usleep_range is preferred over udelay

Fix checkpatch.pl issue:

CHECK: usleep_range is preferred over udelay; see
       Documentation/timers/timers-howto.txt

Replace the udelay() with usleep_range() with a reasonable upper limit.

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>