HID: core: fix memory leak on probe

The dynamically allocted collection stack does not get freed in
all situations. Make sure to also free the collection stack when
using the parser in hid_open_report().

Fixes: 08a8a7cf ("HID: core: do not upper bound the collection stack")
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>