drm/amd/amdgpu: fix null pointer in runtime pm

fix the null pointer issue when runtime pm is triggered.
Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -4866,7 +4866,7 @@ int amdgpu_device_baco_enter(struct drm_device *dev)
 	if (!amdgpu_device_supports_baco(adev_to_drm(adev)))
 		return -ENOTSUPP;
 
-	if (ras && ras->supported)
+	if (ras && ras->supported && adev->nbio.funcs->enable_doorbell_interrupt)
 		adev->nbio.funcs->enable_doorbell_interrupt(adev, false);
 
 	return amdgpu_dpm_baco_enter(adev);
@@ -4885,7 +4885,7 @@ int amdgpu_device_baco_exit(struct drm_device *dev)
 	if (ret)
 		return ret;
 
-	if (ras && ras->supported)
+	if (ras && ras->supported && adev->nbio.funcs->enable_doorbell_interrupt)
 		adev->nbio.funcs->enable_doorbell_interrupt(adev, true);
 
 	return 0;