usb: gadget: udc: renesas_usb3: Fix return value of usb3_write_pipe()

This patch fixes an issue that this driver cannot go status stage
in control read when the req.zero is set to 1 and the len in
usb3_write_pipe() is set to 0. Otherwise, if we use g_ncm driver,
usb enumeration takes long time (5 seconds or more).

Fixes: 746bfe63 ("usb: gadget: renesas_usb3: add support for Renesas USB3.0 peripheral controller")
Cc: <stable@vger.kernel.org> # v4.5+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/renesas_usb3.c

@@ -1038,7 +1038,7 @@ static int usb3_write_pipe(struct renesas_usb3_ep *usb3_ep,
 			usb3_ep->ep.maxpacket);
 	u8 *buf = usb3_req->req.buf + usb3_req->req.actual;
 	u32 tmp = 0;
-	bool is_last;
+	bool is_last = !len ? true : false;
 
 	if (usb3_wait_pipe_status(usb3_ep, PX_STA_BUFSTS) < 0)
 		return -EBUSY;
@@ -1059,6 +1059,7 @@ static int usb3_write_pipe(struct renesas_usb3_ep *usb3_ep,
 		usb3_write(usb3, tmp, fifo_reg);
 	}
 
+	if (!is_last)
 		is_last = usb3_is_transfer_complete(usb3_ep, usb3_req);
 	/* Send the data */
 	usb3_set_px_con_send(usb3_ep, len, is_last);