dmaengine: fsl-edma: Add lockdep assert for exported function

Add lockdep assert for an exported function expected to be called under
spin lock.  Since this function is called in different modules, the
lockdep assert will be self-documenting note about need for locking.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Robin Gong <yibin.gong@nxp.com>
Link: https://lore.kernel.org/r/1591877861-28156-1-git-send-email-krzk@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/fsl-edma-common.c

@@ -589,6 +589,8 @@ void fsl_edma_xfer_desc(struct fsl_edma_chan *fsl_chan)
 {
 	struct virt_dma_desc *vdesc;
 
+	lockdep_assert_held(&fsl_chan->vchan.lock);
+
 	vdesc = vchan_next_desc(&fsl_chan->vchan);
 	if (!vdesc)
 		return;