This simplifies the DMA code a bit by using the dmaengine helpers.
The cookie from descriptor submission can be ignored in this case
as has been established in review of the MMCI/PL180 driver.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>