cma: use be32_to_cpup for devicetree conversion

The value returned by of_get_flat_dt_prop is a pointer. Use
be32_to_cpup which properly type checks against pointers.

Change-Id: Ie75ac6776bd26537a28729902bd918e710eda512
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>

Conflicts:
	drivers/base/dma-contiguous.c