sanitycheck: sanitylib: Fix bare --west-flash option
sanitycheck: sanitylib: Fix bare --west-flash option

If we pass --west-flash with no additional argument that was getting
treated the same as if it wasn't passed at all.

Change the check to be based on 'None' to handle the bare --west-flash
case properly.

Signed-off-by: Kumar Gala <a5e5248af4cd4f0ed8c515f61d40a6e2db46a66e@linaro.org>

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