dmaengine: xilinx: vdma: Check if the segment list is empty in a descriptor

The segment list in a descriptor should be checked for empty, else
it will try to access invalid address for the first call.  This
patch fixes this issue.
Signed-off-by: Srikanth Thokala <sthokal@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/xilinx/xilinx_vdma.c

@@ -971,9 +971,11 @@ xilinx_vdma_dma_prep_interleaved(struct dma_chan *dchan,
 		hw->buf_addr = xt->src_start;
 
 	/* Link the previous next descriptor to current */
-	prev = list_last_entry(&desc->segments,
-				struct xilinx_vdma_tx_segment, node);
-	prev->hw.next_desc = segment->phys;
+	if (!list_empty(&desc->segments)) {
+		prev = list_last_entry(&desc->segments,
+				       struct xilinx_vdma_tx_segment, node);
+		prev->hw.next_desc = segment->phys;
+	}
 
 	/* Insert the segment into the descriptor segments list. */
 	list_add_tail(&segment->node, &desc->segments);