usb_dc_stm32: improve struct layout.
usb_dc_stm32: improve struct layout.

Put the one-byte sized fields next to each other to reduce padding.

Signed-off-by: Josh Gao <c028c213ed5efcf30c3f4fc7361dbde0c893c5b7@jmgao.dev>

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