HID: hid-multitouch: Remove misleading null test

A null test was left behind during the autoloading work;
the test was introduced by 8d179a9e

, but was never completely
reverted.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>