staging: ion: ion_cma_heap: Don't directly use dma_common_get_sgtable

Use dma_get_sgtable rather than dma_common_get_sgtable so a device's
dma_ops aren't bypassed. This is essential in situations where a device
uses an IOMMU and the physical memory is not contiguous (as the common
function assumes).

Signed-off-by: Jon Medhurst <tixy@linaro.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>