drm/msm: Offset MDSS HBB value by 13

The Adreno part of the driver exposes this value to userspace, and the
SMEM data source also presents a x+13 value. Keep things coherent and
make the value uniform across them.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/660961/


Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>