dmaengine: virt-dma: vchan_find_desc()

Add a function to find a descriptor within the depths of the
virtualized DMA channel support.  Needed for tx_status functionality.

Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h
index 825bb96..44ec57e 100644
--- a/drivers/dma/virt-dma.h
+++ b/drivers/dma/virt-dma.h
@@ -40,8 +40,8 @@
 }
 
 void vchan_dma_desc_free_list(struct virt_dma_chan *vc, struct list_head *head);
-
 void vchan_init(struct virt_dma_chan *vc, struct dma_device *dmadev);
+struct virt_dma_desc *vchan_find_desc(struct virt_dma_chan *, dma_cookie_t);
 
 /**
  * vchan_tx_prep - prepare a descriptor