iommu/dma: Restore scatterlist offsets correctly

With the change to stashing just the IOVA-page-aligned remainder of the
CPU-page offset rather than the whole thing, the failure path in
__invalidate_sg() also needs tweaking to account for that in the case of
differing page sizes where the two offsets may not be equivalent.
Similarly in __finalise_sg(), lest the architecture-specific wrappers
later get the wrong address for cache maintenance on sync or unmap.

Fixes: 164afb1d

 ("iommu/dma: Use correct offset in map_sg")
Reported-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Cc: stable@ver.kernel.org # v4.4+
Signed-off-by: Joerg Roedel <jroedel@suse.de>