HID: wiimote: fix nunchuck button parser

The buttons of the Wii Remote Nunchuck extension are actually active low.
Fix the parser to forward the inverted values. The comment in the function
always said "0 == pressed" but the implementation was wrong from the
beginning.

Cc: stable@vger.kernel.org
Reported-by: Victor Quicksilver <victor.quicksilver@gmail.com>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>