drm/msm/a6xx: Improve a6xx_bus_clear_pending_transactions()

Unify the indentation and explain the cryptic 0xF value.

Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/542756/


Signed-off-by: Rob Clark <robdclark@chromium.org>