The new AMD IOMMU DMA implementation concatenates sglist entries under
certain conditions, and because saa7146 accessed the length member
directly, it did not support this scenario.

This fixes IO_PAGE_FAULTs by using the sg_dma_len macro.

Fixes: be62dbf5 ("iommu/amd: Convert AMD iommu driver to the dma-iommu api")
Signed-off-by: Tasos Sahanidis <tasos@tasossah.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>