dmaengine: imx-dma: fix missing unlock on error in imxdma_xfer_desc()

Add the missing unlock on the error handling path in function
imxdma_xfer_desc().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>

drivers/dma/imx-dma.c

@@ -474,8 +474,10 @@ static int imxdma_xfer_desc(struct imxdma_desc *d)
 			slot = i;
 			break;
 		}
-		if (slot < 0)
+		if (slot < 0) {
+			spin_unlock_irqrestore(&imxdma->lock, flags);
 			return -EBUSY;
+		}
 
 		imxdma->slots_2d[slot].xsr = d->x;
 		imxdma->slots_2d[slot].ysr = d->y;