HID: hid-lg4ff: Make lg4ff_wheel_data a separate structure

Make lg4ff_wheel_data a separate structure stored within lg4ff_device_entry.
Adjust the initialization process accordingly.
Signed-off-by: Michal Malý <madcatxster@devoid-pointer.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>