intel-iommu: mark intel_dma_ops static

ia64 currently explicitly assigns it to dma_ops, but that same work is
already done by intel_iommu_init a little later, so we can remove the
duplicate assignment and mark the variable static.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>