drivers: spi: Fix `spi_loopback` failure for Renesas RZ/G3S-SMARC

Fixes the `spi_loopback` test failure on board Renesas `rzg3s_smarc` since
the test has been updated by zephyrproject-rtos/zephyr/pull/86383

Signed-off-by: Quang Le <quang.le.eb@bp.renesas.com>
Signed-off-by: Tien Nguyen <tien.nguyen.zg@renesas.com>