stm32_common/gpio: fix pin in gpio_init_init
stm32_common/gpio: fix pin in gpio_init_init

Clearing pending interrupts and enabling them for a certain pin
used the wrong variable, this is fixed here.

RIOT-OS/RIOT,x3ro/RIOT,aeneby/RIOT,mtausig/RIOT,OlegHahm/RIOT,toonst/RIOT,rfuentess/RIOT,mtausig/RIOT,jasonatran/RIOT,basilfx/RIOT,jasonatran/RIOT,rfuentess/RIOT,toonst/RIOT,mfrey/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,authmillenon/RIOT,kaspar030/RIOT,yogo1212/RIOT,yogo1212/RIOT,toonst/RIOT,smlng/RIOT,basilfx/RIOT,rfuentess/RIOT,mfrey/RIOT,cladmi/RIOT,miri64/RIOT,basilfx/RIOT,OTAkeys/RIOT,smlng/RIOT,OTAkeys/RIOT,josephnoir/RIOT,josephnoir/RIOT,x3ro/RIOT,basilfx/RIOT,kaspar030/RIOT,OlegHahm/RIOT,aeneby/RIOT,miri64/RIOT,kaspar030/RIOT,mtausig/RIOT,miri64/RIOT,cladmi/RIOT,yogo1212/RIOT,x3ro/RIOT,authmillenon/RIOT,kaspar030/RIOT,x3ro/RIOT,kYc0o/RIOT,mtausig/RIOT,josephnoir/RIOT,mfrey/RIOT,authmillenon/RIOT,ant9000/RIOT,OlegHahm/RIOT,basilfx/RIOT,ant9000/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,rfuentess/RIOT,mtausig/RIOT,yogo1212/RIOT,authmillenon/RIOT,aeneby/RIOT,OlegHahm/RIOT,kYc0o/RIOT,miri64/RIOT,rfuentess/RIOT,authmillenon/RIOT,mfrey/RIOT,yogo1212/RIOT,jasonatran/RIOT,miri64/RIOT,ant9000/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,ant9000/RIOT,OTAkeys/RIOT,josephnoir/RIOT,aeneby/RIOT,cladmi/RIOT,kaspar030/RIOT,OTAkeys/RIOT,cladmi/RIOT,kYc0o/RIOT,smlng/RIOT,cladmi/RIOT,mfrey/RIOT,aeneby/RIOT,x3ro/RIOT,toonst/RIOT,smlng/RIOT,josephnoir/RIOT,jasonatran/RIOT,kYc0o/RIOT,smlng/RIOT,OTAkeys/RIOT,toonst/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT