usb-gadget: unlock data->lock mutex on error path in ep_write()

ep_write() acquires data->lock mutex in get_ready_ep() and releases it
on all paths except for one: when usb_endpoint_xfer_isoc() failed. The
patch adds mutex_unlock(&data->lock) at that path.

It is similar to commit 00cc7a5f ("usb-gadget: unlock data->lock mutex on error path in ep_read()"),
it was not fixed at that time by accident.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/inode.c

@@ -431,8 +431,10 @@ ep_write (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 
 	/* halt any endpoint by doing a "wrong direction" i/o call */
 	if (!usb_endpoint_dir_in(&data->desc)) {
-		if (usb_endpoint_xfer_isoc(&data->desc))
+		if (usb_endpoint_xfer_isoc(&data->desc)) {
+			mutex_unlock(&data->lock);
 			return -EINVAL;
+		}
 		DBG (data->dev, "%s halt\n", data->name);
 		spin_lock_irq (&data->dev->lock);
 		if (likely (data->ep != NULL))