drm/amdgpu: clean doorbell after sending init table to mmsch

According to HW design, need to clean doorbell after setup MMSCH
table.

Signed-off-by: Frank Min <Frank.Min@amd.com>
Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Reviewed-by: Monk Liu <Monk.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/uvd_v7_0.c

@@ -702,6 +702,7 @@ static int uvd_v7_0_mmsch_start(struct amdgpu_device *adev,
 		dev_err(adev->dev, "failed to init MMSCH, mmVCE_MMSCH_VF_MAILBOX_RESP = %x\n", data);
 		return -EBUSY;
 	}
+	WDOORBELL32(adev->uvd.ring_enc[0].doorbell_index, 0);
 
 	return 0;
 }

drivers/gpu/drm/amd/amdgpu/vce_v4_0.c

@@ -190,6 +190,7 @@ static int vce_v4_0_mmsch_start(struct amdgpu_device *adev,
 		dev_err(adev->dev, "failed to init MMSCH, mmVCE_MMSCH_VF_MAILBOX_RESP = %x\n", data);
 		return -EBUSY;
 	}
+	WDOORBELL32(adev->vce.ring[0].doorbell_index, 0);
 
 	return 0;
 }