Bug Fix arch/ia64/kernel/pci-dma.c: fix recursive dma_supported() call in iommu_dma_supported()

In commit 160c1d8e

,
dma_ops->dma_supported = iommu_dma_supported;

This dma_ops->dma_supported is first called in platform_dma_init() during kernel
boot. Then dma_ops->dma_supported will be called recursively in
iommu_dma_supported.

Kernel can not boot because kernel can not get out of iommu_dma_supported until
it runs out of stack memory.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>