HID: core: simplify active collection tracking

Manually tracking an active collection to set collection parents is not
necessary, we just have to look one step back into the collection stack
to find the correct parent.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>