intel-iommu.c: dma ops fix

Stephen Rothwell noticed that:

Commit 2be62149

 ("x86: dma-ops on highmem
fix") in Linus' tree introduced a new warning (noticed in the x86_64
allmodconfig build of linux-next):

drivers/pci/intel-iommu.c:2240: warning: initialization from incompatible pointer type

Which points at an instance of map_single that needs updating.

Fix it to the new prototype.

Signed-off-by: Ingo Molnar <mingo@elte.hu>