zephyr: fix flash_area_erase()
zephyr: fix flash_area_erase()

Flash must be unlocked before it can be erased.

Signed-off-by: Marti Bolivar <9d90ac4c7bf6a305f6bfd81a23c7859bc883380e@linaro.org>

ATmobica/mcuboot,ATmobica/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,utzig/mcuboot,runtimeco/mcuboot,tamban01/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,utzig/mcuboot,utzig/mcuboot,tamban01/mcuboot,ATmobica/mcuboot,utzig/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,utzig/mcuboot