drm/msm: fix unbalanced pm_runtime_enable in adreno_gpu_{init, cleanup}

adreno_gpu_init calls pm_runtime_enable, so adreno_gpu_cleanup needs to
call pm_runtime_disable.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Rob Clark <robdclark@chromium.org>