Input: aiptek - do not check for NULL in attribute methods

It makes no sense to check for NULL in attribute methods -
we do usb_set_intfdata before creating attributes and once
attributes have been removed we are guaranteed to not be
called.

Signed-off-by: Rene van Paassen <rene.vanpaassen@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>