HID: wiimote: Cache wiimote led state

Save the current state of the leds in the wiimote data structure. This
allows us to discard new led requests that wouldn't change anything.
Protect the whole state structure by a spinlock. Every wiiproto_*
function expects this spinlock to be held when called.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>