MALI: Fix possible use after free of task_struct

Move to using the mm from the task, with reference counting, instead of
storing the task_struct pointer.

BUG=chromium:609382
TEST=run aquarium on daisy
TEST=run test.c from ticket

Change-Id: I4f8d1761a2286c5e8bce829ee3ff5aa2826fdf65
Reviewed-on: https://chromium-review.googlesource.com/343880
Commit-Ready: Stéphane Marchesin <marcheu@chromium.org>
Tested-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Ricky Zhou <rickyz@chromium.org>
4 files changed