usb: renesas_usbhs: bugfix: add .release function to gpriv->gadget.dev

This patch fixup below warning on device_unregister()

renesas_usbhs renesas_usbhs.1: host probed
renesas_usbhs renesas_usbhs.1: gadget probed
renesas_usbhs renesas_usbhs.1: irq request err
------------[ cut here ]------------
WARNING: at ${LINUX}/drivers/base/core.c:1)
Device 'gadget' does not have a release() function, it is broken and must be fi.
Modules linked in:
[<c000e25c>] (unwind_backtrace+0x0/0xe4) from [<c0016960>] (warn_slowpath_commo)
[<c0016960>] (warn_slowpath_common+0x4c/0x64) from [<c00169f8>] (warn_slowpath_)
[<c00169f8>] (warn_slowpath_fmt+0x2c/0x3c) from [<c0185b80>] (device_release+0x)
[<c0185b80>] (device_release+0x70/0x84) from [<c013e300>] (kobject_cleanup+0x58)
[<c013e300>] (kobject_cleanup+0x58/0x6c) from [<c01cba14>] (usbhs_mod_gadget_re)
[<c01cba14>] (usbhs_mod_gadget_remove+0x3c/0x6c) from [<c01c8384>] (usbhs_mod_p)
[<c01c8384>] (usbhs_mod_probe+0x68/0x80) from [<c01c7f84>] (usbhs_probe+0x1cc/0)
...

Cc: stable@vger.kernel.org
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/renesas_usbhs/mod_gadget.c

@@ -941,6 +941,11 @@ static int usbhsg_stop(struct usbhs_priv *priv)
 	return usbhsg_try_stop(priv, USBHSG_STATUS_STARTED);
 }
 
+static void usbhs_mod_gadget_release(struct device *pdev)
+{
+	/* do nothing */
+}
+
 int usbhs_mod_gadget_probe(struct usbhs_priv *priv)
 {
 	struct usbhsg_gpriv *gpriv;
@@ -989,6 +994,7 @@ int usbhs_mod_gadget_probe(struct usbhs_priv *priv)
 	 */
 	dev_set_name(&gpriv->gadget.dev, "gadget");
 	gpriv->gadget.dev.parent	= dev;
+	gpriv->gadget.dev.release	= usbhs_mod_gadget_release;
 	gpriv->gadget.name		= "renesas_usbhs_udc";
 	gpriv->gadget.ops		= &usbhsg_gadget_ops;
 	gpriv->gadget.max_speed		= USB_SPEED_HIGH;