drm/amdgpu: fix sdma firmware version error in sriov

Re-adjust the function return order to avoid empty sdma version in the
sriov environment. (read amdgpu_firmware_info)

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Stanley.Yang <Stanley.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>