drivers: usb_dc_mcux_ehci: fix style, rework usb_dc_attach
drivers: usb_dc_mcux_ehci: fix style, rework usb_dc_attach

Fix style, rework usb_dc_attach.

Signed-off-by: Johann Fischer <b39b26e1812eb092eb217277792f3735321fa456@phytec.de>

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