drm/amdgpu: value of amdgpu_sriov_vf cannot be set into F32_POLL_ENABLE

amdgpu_sriov_vf would return 0x0 or 0x4 to indicate if sriov.
but F32_POLL_ENABLE need 0x0 or 0x1 to determine if enabled.
set 0x4 into F32_POLL_ENABLE would make SDMA0_GFX_RB_WPTR_POLL_CNTL not working.

Signed-off-by: Wentao Lou <Wentao.Lou@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>