ARM: dma-mapping: fix GFP_ATOMIC macro usage

GFP_ATOMIC is not a single gfp flag, but a macro which expands to the other
flags and LACK of __GFP_WAIT flag. To check if caller wanted to perform an
atomic allocation, the code must test __GFP_WAIT flag presence. This patch
fixes the issue introduced in v3.6-rc5

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
CC: stable@vger.kernel.org