subsys: fs/nvs: never read more than the destination buffer
subsys: fs/nvs: never read more than the destination buffer

Reading more than the destination buffer means that data is overwritten
possibly on the stack. This causes unpredictable behaviours like
crashes.

Signed-off-by: Aurelien Jarno <bceb368e7f2cb351af47298f32034f0587bbe4a6@aurel32.net>

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