HID: wiimote: Simplify synchronization

The new locking scheme in HID core allows us to remove a bit of synchronization.
Since the HID layer acts synchronously we simply register input core last and
there are no synchonization issues anymore.
Also register sysfs files after that to simplify the code.

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