drm/amdgpu: check mmhub_funcs pointer before refering to it

mmhub callback functions are not initialized for all the ASICs
Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c

@@ -799,7 +799,7 @@ static int gmc_v9_0_ecc_late_init(void *handle)
 			goto umc_late_fini;
 	}
 
-	if (adev->mmhub_funcs->ras_late_init) {
+	if (adev->mmhub_funcs && adev->mmhub_funcs->ras_late_init) {
 		r = adev->mmhub_funcs->ras_late_init(adev);
 		if (r)
 			return r;