HID: hid-lg4ff: add a kfree() to an error path

There is a small rare potential memory leak here.  Also Walter Harms
points out that we can do a small cleanup as well by using kstrdup().

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>