backend: touch: Fixup incomplete patch for single touch devices.
backend: touch: Fixup incomplete patch for single touch devices.

All instances of libinput_event_touch_get_slot need to be converted to
libinput_event_touch_get_seat_slot for things to work.

ascent12/wlroots,swaywm/wlroots,swaywm/wlroots,ascent12/wlroots,SirCmpwn/wlroots