HID: extend mask for BUTTON usage page

Now that joystick button usages can expand over 15 buttons, we
have to properly mask out the code from hid usage to cover the
whole 0xffff available space.

Reported-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>