fcb: Fix parameter description
fcb: Fix parameter description

Function writes to, not reads from flash.

Signed-off-by: Reto Schneider <cd29db203813b56a5006d9884d446b92bc63b915@husqvarnagroup.com>

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