[PATCH 4/4] i915: fix remap_io_sg to verify the pgprot

[Serge Belyshev]

I have another problem with this patch since it landed in mainline. On
my m3-6Y30 skylake HD Graphics 515 (rev 07), it causes visual artifacts
that look like bunch of one pixel high horizontal streaks, seen most
often in firefox while scrolling or in menu controls.

Reverting this patch on top of current mainline fixes the problem.