dma-trace: avoid multiple allocations to fix fuzzy IPC

The fuzzy IPC testing reports there is memory leak if dma_trace_config
IPC is sent multiple times, we should just return if the DMA trace
buffer is already allocated, to avoid allocating new buffers and the
leakage of the old buffers.

Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>

Author: keyonjie

src/trace/dma-trace.c

@@ -407,6 +407,10 @@ int dma_trace_enable(struct dma_trace_data *d)
 {
 	int err;
 
+	/* the existence of the trace buffer means the dma trace already initialized */
+	if (d->dmatb.addr)
+		return 0;
+
 	/* initialize dma trace buffer */
 	err = dma_trace_buffer_init(d);