selftests: hid: attach/detach 2 bpf programs, not just one

Add a second BPF program to attach to the device, as the development of
this feature showed that we also need to ensure we can detach multiple
programs to a device (hid_bpf_link->hid_table_index was actually not set
initially, and this lead to any BPF program not being released except for
the first one).

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>