edma: do not waste memory for dma_mask

Accordingly to commentary in the platform_device_register_full the memory
allocated for dma_mask will not going to be freed. That's why is better to
assign dma_mask afterwards.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>