usb: musb: check for zero byte in musb_read/write_fifo

Added a check in musb_{read | write}_fifo for zero byte length.
Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_core.c

@@ -234,6 +234,9 @@ void musb_write_fifo(struct musb_hw_ep *hw_ep, u16 len, const u8 *src)
 	struct musb *musb = hw_ep->musb;
 	void __iomem *fifo = hw_ep->fifo;
 
+	if (unlikely(len == 0))
+		return;
+
 	prefetch((u8 *)src);
 
 	dev_dbg(musb->controller, "%cX ep%d fifo %p count %d buf %p\n",
@@ -276,6 +279,9 @@ void musb_read_fifo(struct musb_hw_ep *hw_ep, u16 len, u8 *dst)
 	struct musb *musb = hw_ep->musb;
 	void __iomem *fifo = hw_ep->fifo;
 
+	if (unlikely(len == 0))
+		return;
+
 	dev_dbg(musb->controller, "%cX ep%d fifo %p count %d buf %p\n",
 			'R', hw_ep->epnum, fifo, len, dst);