drm/msm/a6xx: Use "else if" in GPU speedbin rev matching

The GPU can only be one at a time. Turn a series of ifs into if +
elseifs to save some CPU cycles.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/542770/


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