drm/amdgpu: use helper in amdgpu_gart_unbind

When amdgpu_gart_invalidate_tlb helper is introduced this part was left
out of the conversion. Avoid the code duplication here.
Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -325,10 +325,7 @@ void amdgpu_gart_unbind(struct amdgpu_device *adev, uint64_t offset,
 			page_base += AMDGPU_GPU_PAGE_SIZE;
 		}
 	}
-	mb();
-	amdgpu_device_flush_hdp(adev, NULL);
-	for_each_set_bit(i, adev->vmhubs_mask, AMDGPU_MAX_VMHUBS)
-		amdgpu_gmc_flush_gpu_tlb(adev, 0, i, 0);
+	amdgpu_gart_invalidate_tlb(adev);
 
 	drm_dev_exit(idx);
 }