drm/msm/a7xx: actually use a7xx state registers

Make a6xx_get_registers() use a7xx registers instead of a6xx ones if the
detected Adreno is from the A7xx family.

Fixes: e997ae5f

 ("drm/msm/a6xx: Mostly implement A7xx gpu_state")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/562233/
Signed-off-by: Rob Clark <robdclark@chromium.org>