drm/msm/a5xx: Fix VPC protect value in gpu_write()

The upstream API for some reason uses logbase2 instead of
just passing the argument as-is, whereas downstream CAF
kernel does the latter.

Hence, a mistake has been made when porting:
4 is the value that's supposed to be passed, but
log2(4) = 2. Changing the value to 16 (= 2^4) fixes
the issue.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>