dmaengine: virt-dma: Add missing locking around list operations

All list operations are protected by &vc->lock. As vchan_vdesc_fini()
is called unlocked add the missing locking around the list operations.

Signed-off-by: Sascha Hauer <[e-mail]>
Reviewed-by: Peter Ujfalusi <[e-mail]>
Tested-by: Peter Ujfalusi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/virt-dma.h

···
 {
 	struct virt_dma_chan *vc = to_virt_chan(vd->tx.chan);
 
-	if (dmaengine_desc_test_reuse(&vd->tx))
+	if (dmaengine_desc_test_reuse(&vd->tx)) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&vc->lock, flags);
 		list_add(&vd->node, &vc->desc_allocated);
-	else
+		spin_unlock_irqrestore(&vc->lock, flags);
+	} else {
 		vc->desc_free(vd);
+	}
 }
 
 /**