drm/amdgpu: Skip ring soft recovery when fence was NULL

amdgpu_ring_soft_recovery would have Call-Trace,
when s_fence->parent was NULL inside amdgpu_job_timedout.
Check fence first, as drm_sched_hw_job_reset did.
Signed-off-by: NWentao Lou <Wentao.Lou@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

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

@@ -397,7 +397,7 @@ bool amdgpu_ring_soft_recovery(struct amdgpu_ring *ring, unsigned int vmid,
 {
 	ktime_t deadline = ktime_add_us(ktime_get(), 10000);
 
-	if (!ring->funcs->soft_recovery)
+	if (!ring->funcs->soft_recovery || !fence)
 		return false;
 
 	atomic_inc(&ring->adev->gpu_reset_counter);