usb: Fix qcserial memory leak on rmmod

qcprobe function allocates serial->private but this is never freed, this
patch adds a new function qc_release() which frees serial->private, after
calling usb_wwan_release
Signed-off-by: Steven Hardy <shardy@redhat.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/qcserial.c

@@ -205,6 +205,18 @@ static int qcprobe(struct usb_serial *serial, const struct usb_device_id *id)
 	return retval;
 }
 
+static void qc_release(struct usb_serial *serial)
+{
+	struct usb_wwan_intf_private *priv = usb_get_serial_data(serial);
+
+	dbg("%s", __func__);
+
+	/* Call usb_wwan release & free the private data allocated in qcprobe */
+	usb_wwan_release(serial);
+	usb_set_serial_data(serial, NULL);
+	kfree(priv);
+}
+
 static struct usb_serial_driver qcdevice = {
 	.driver = {
 		.owner     = THIS_MODULE,
@@ -222,7 +234,7 @@ static struct usb_serial_driver qcdevice = {
 	.chars_in_buffer     = usb_wwan_chars_in_buffer,
 	.attach		     = usb_wwan_startup,
 	.disconnect	     = usb_wwan_disconnect,
-	.release	     = usb_wwan_release,
+	.release	     = qc_release,
 #ifdef CONFIG_PM
 	.suspend	     = usb_wwan_suspend,
 	.resume		     = usb_wwan_resume,