drm/amdgpu/gfx9: fix compute ring doorbell index

This got lost when the code was revamped.  Copy/paste bug from
gfx8.
Reported-by: Evan Quan <evan.quan@amd.com>
Fixes: 78c16834 (drm/amdgpu: allow split of queues with kfd at queue granularity v4)
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c

@@ -1281,7 +1281,7 @@ static int gfx_v9_0_compute_ring_init(struct amdgpu_device *adev, int ring_id,
 
 	ring->ring_obj = NULL;
 	ring->use_doorbell = true;
-	ring->doorbell_index = AMDGPU_DOORBELL_MEC_RING0 + ring_id;
+	ring->doorbell_index = (AMDGPU_DOORBELL_MEC_RING0 + ring_id) << 1;
 	ring->eop_gpu_addr = adev->gfx.mec.hpd_eop_gpu_addr
 				+ (ring_id * GFX9_MEC_HPD_SIZE);
 	sprintf(ring->name, "comp_%d.%d.%d", ring->me, ring->pipe, ring->queue);