USB: option: Use generic USB wwan code

As this code was simply factored out of option, this is a simple
conversion.
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/Kconfig

@@ -581,6 +581,7 @@ config USB_SERIAL_WWAN
 
 config USB_SERIAL_OPTION
 	tristate "USB driver for GSM and CDMA modems"
+	select USB_SERIAL_WWAN
 	help
 	  Say Y here if you have a GSM or CDMA modem that's connected to USB.