native_posix: Add flags to fs_open invocation
native_posix: Add flags to fs_open invocation

Added flags that were missing from fs_open() call.

Signed-off-by: Mattias Säteri <3c7968627e814b7eac2aa67b770f29a943bb222c@flir.com>

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