ARM: 7857/1: dma: imx-sdma: setup dma mask

The dma mask is not configured in the current code.
This was triggered by soc-dmaengine-pcm which allocate the dma
buffers with the imx-sdma as device.
This commit fix audio on imx31.

Signed-off-by: Philippe Rétornaz <philippe.retornaz@epfl.ch>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>