Input: scancode in get/set_keycodes should be unsigned

The HID layer has some scan codes of the form 0xffbc0000 for logitech
devices which do not work if scancode is typed as signed int, so we need
to switch to unsigned it instead. While at it keycode being signed does
not make much sense either.

Acked-by: Márton Németh <nm127@freemail.hu>
Acked-by: Matthew Garrett <mjg@redhat.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>