usb: set data stage length variable to zero by default
usb: set data stage length variable to zero by default

Set data stage length variable to zero as a precaution
so that no trouble happens if control request handler
does not check the request values sufficiently.

Signed-off-by: Johann Fischer <64a5f06fca6b2d93d742efe564789153170f6198@nordicsemi.no>

galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr