drm/amdgpu/powerplay: silence a warning in smu_v11_0_setup_pptable

I think gcc is confused as I don't see how size could be used
unitialized, but go ahead and silence the warning.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190822032527.1376-1-alexander.deucher@amd.com