HID: hid-lg4ff: Allow the driver to continue without sysfs interface

Allow the driver to continue without sysfs interface. Instead of bailing out
allow the driver to continue in a degraded mode.

Signed-off-by: Michal Malý <madcatxster@devoid-pointer.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>