drm/amdgpu/smu11: fix warning on 32bit arches

Fixes
warning: cast from pointer to integer of different size
[-Wpointer-to-int-cast]
on 32 bit platforms.

Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>