usb: mtu3: fix EXTCON dependency

When EXTCON is a loadable module, mtu3 fails to link as built-in:

drivers/usb/mtu3/mtu3_plat.o: In function `mtu3_probe':
mtu3_plat.c:(.text+0x690): undefined reference to `extcon_get_edev_by_phandle'

Add a Kconfig dependency to force mtu3 also to be a loadable module
if extconn is, but still allow it to be built without extcon.

Fixes: d0ed062a ("usb: mtu3: dual-role mode support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/mtu3/Kconfig

@@ -6,6 +6,7 @@ config USB_MTU3
 	tristate "MediaTek USB3 Dual Role controller"
 	depends on USB || USB_GADGET
 	depends on ARCH_MEDIATEK || COMPILE_TEST
+	depends on EXTCON || !EXTCON
 	select USB_XHCI_MTK if USB_SUPPORT && USB_XHCI_HCD
 	help
 	  Say Y or M here if your system runs on MediaTek SoCs with