drm/amdgpu: fix uninitialized variable warning for sdma_v7

Clear warning that using uninitialized variable index.
Signed-off-by: Tim Huang <Tim.Huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/sdma_v7_0.c

@@ -876,6 +876,7 @@ static int sdma_v7_0_ring_test_ring(struct amdgpu_ring *ring)
 	r = amdgpu_ring_alloc(ring, 5);
 	if (r) {
 		DRM_ERROR("amdgpu: dma failed to lock ring %d (%d).\n", ring->idx, r);
+		if (!ring->is_mes_queue)
 			amdgpu_device_wb_free(adev, index);
 		return r;
 	}