drm/amdgpu: Initialize timestamp for some legacy SOCs

Initialize the interrupt timestamp for some legacy SOCs
to fix the coverity issue "Uninitialized scalar variable"
Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Suggested-by: Christian König <christian.koenig@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_irq.c

@@ -445,6 +445,14 @@ void amdgpu_irq_dispatch(struct amdgpu_device *adev,
 
 	entry.ih = ih;
 	entry.iv_entry = (const uint32_t *)&ih->ring[ring_index];
+
+	/*
+	 * timestamp is not supported on some legacy SOCs (cik, cz, iceland,
+	 * si and tonga), so initialize timestamp and timestamp_src to 0
+	 */
+	entry.timestamp = 0;
+	entry.timestamp_src = 0;
+
 	amdgpu_ih_decode_iv(adev, &entry);
 
 	trace_amdgpu_iv(ih - &adev->irq.ih, &entry);