HID: lg4ff: Remove sysfs iface before deallocating memory

This patch fixes a possible race condition caused by the sysfs
interface being removed after the memory used by the interface
was already kfree'd.

Signed-off-by: Michal Malý <madcatsxter@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>