cpu/esp8266: fix `esp_sw_timer` compile problem
cpu/esp8266: fix `esp_sw_timer` compile problem


kaspar030/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,kYc0o/RIOT,jasonatran/RIOT,kaspar030/RIOT,miri64/RIOT,ant9000/RIOT,jasonatran/RIOT,miri64/RIOT,kYc0o/RIOT,OlegHahm/RIOT,ant9000/RIOT,ant9000/RIOT,kYc0o/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,kYc0o/RIOT,ant9000/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,miri64/RIOT,OlegHahm/RIOT,jasonatran/RIOT,miri64/RIOT,miri64/RIOT,kaspar030/RIOT,kYc0o/RIOT