drm/msm/a6xx: fix a potential overflow issue

drm/msm/a6xx: fix a potential overflow issue

BugLink: https://bugs.launchpad.net/bugs/1902115
[ Upstream commit 08d3ab4b46339bc6f97e83b54a3fb4f8bf8f4cd9 ]

It's allocating an array of a6xx_gpu_state_obj structure rathor than
its pointers.

This patch fix it.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Ian May <ian.may@canonical.com>