drm/msm/adreno: fix sparse warnings in a6xx code

drm/msm/adreno: fix sparse warnings in a6xx code

Sparse reports plenty of warnings against the a6xx code because of
a6xx_gmu::mmio and a6xx_gmu::rscc members. For some reason they were
defined as __iomem pointers rather than pointers to __iomem memory.
Correct the __iomem attribute.

Fixes: 02ef80c54e7c ("drm/msm/a6xx: update pdc/rscc GMU registers for A640/A650")
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202304070550.NrbhJCvP-lkp@intel.com/
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/531583/
Signed-off-by: Rob Clark <robdclark@chromium.org>