boards: arm: b_l4s5i_iot01a: SPI chip-select is active low.
boards: arm: b_l4s5i_iot01a: SPI chip-select is active low.

According to RM0432, the chip-select of SPI is active low.

Fixes #36289

Signed-off-by: Sam Chen <14d33955d1f7249226a773652e330df198f5a351@iota.org>

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