boards: nucleo_l432kc: Fix comment on partition description
boards: nucleo_l432kc: Fix comment on partition description

Comment for storage partition could be misleading.
Clarify this is a partition used for file system.

Signed-off-by: Erwan Gouriou <de4d967452b83bb0e37525652734e7d9163b6a4c@linaro.org>

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