Bluetooth: hidp: implement hidinput_input_event callback

We can re-enable hidinput_input_event to allow the leds of bluetooth
keyboards to be set.
Now the callbacks uses hid core to retrieve the right HID report to
send, so this version is safer.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>