samples: drivers: soc_flash_nrf5 fix missing flash write access
samples: drivers: soc_flash_nrf5 fix missing flash write access

By default CONFIG_MPU_ALLOW_FLASH_WRITE=n so the example must have been
falling on any write to flash.
This patch adds CONFIG_MPU_ALLOW_FLASH_WRITE=y to project configuration.

Signed-off-by: Andrzej Puzdrowski <0222c24e1773dd88269ed0e559909ec9bea3604a@nordicsemi.no>

punitvara/zephyr,explora26/zephyr,punitvara/zephyr,nashif/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyriot/zephyr,mbolivar/zephyr,zephyriot/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,kraj/zephyr,ldts/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,kraj/zephyr,mbolivar/zephyr,ldts/zephyr,explora26/zephyr,kraj/zephyr,Vudentz/zephyr,Vudentz/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,mbolivar/zephyr,Vudentz/zephyr,Vudentz/zephyr,punitvara/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,punitvara/zephyr,finikorg/zephyr,mbolivar/zephyr,galak/zephyr,mbolivar/zephyr,ldts/zephyr,galak/zephyr,zephyriot/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr