iommu/intel: small map_page cleanup

Pass the page + offset to the low-level __iommu_map_single helper
(which gets renamed to fit the new calling conventions) as both
callers have the page at hand.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>