drm/amdgpu: Fix for MEC SJT FW Load Fail on VF

Users might switch to ROCM build does not include MEC SJT FW and driver
needs to consider this case.w

Signed-off-by: yfeng1 <yfeng1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>