ARM: dma-mapping: Get pages if the cpu_addr is out of atomic_pool

In __iommu_get_pages(), the cpu_addr is checked wheather in
atomic_pool range or not. So if the cpu_addr is in atomic_pool
range, it does not need to check twice.

Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>