i915: align in pixels not bytes on gen3

BUG=chromium:428125
TEST=freon on zgb runs a bit further

Change-Id: I9bac0871ba4e04e3a3d5ff1579a119987d889e61
Reviewed-on: https://chromium-review.googlesource.com/263288
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Commit-Queue: Stéphane Marchesin <marcheu@chromium.org>
Tested-by: Stéphane Marchesin <marcheu@chromium.org>
1 file changed