staging: comedi: das1800: tidy up das1800_init_dma()

Refactor this function so that a for loop can be used to request and
set up the two DMA descriptors.

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>

diff --cc drivers/staging/comedi/drivers/das1800.c
Simple merge