drm/amdgpu: psp_ring_destroy cause psp->km_ring.ring_mem NULL

psp_ring_destroy inside psp_load_fw cause psp->km_ring.ring_mem NULL.
Call Trace occurred when psp_cmd_submit.
should be psp_ring_stop instead.
Reviewed-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Signed-off-by: Wentao Lou <Wentao.Lou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -547,7 +547,7 @@ static int psp_load_fw(struct amdgpu_device *adev)
 	struct psp_context *psp = &adev->psp;
 
 	if (amdgpu_sriov_vf(adev) && adev->in_gpu_reset) {
-		psp_ring_destroy(psp, PSP_RING_TYPE__KM);
+		psp_ring_stop(psp, PSP_RING_TYPE__KM); /* should not destroy ring, only stop */
 		goto skip_memalloc;
 	}