drm/amdgpu: Log RAS errors during load

During driver load, RAS event manager may not be initialized. This will
cause any ATHUB event during driver load to be skipped in dmesg log. Log
the error in dmesg log for easier diagnosis.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>