usb: musb: cppi41: fix missing unlock on error in cppi41_dma_callback()

Add the missing unlock before return from function cppi41_dma_callback()
in the error handling case.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_cppi41.c

@@ -150,8 +150,10 @@ static void cppi41_dma_callback(void *private_data)
 				remain_bytes,
 				direction,
 				DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
-		if (WARN_ON(!dma_desc))
+		if (WARN_ON(!dma_desc)) {
+			spin_unlock_irqrestore(&musb->lock, flags);
 			return;
+		}
 
 		dma_desc->callback = cppi41_dma_callback;
 		dma_desc->callback_param = channel;