USB: input: aiptek.c: fix up dev_err() usage

We should always reference the input device for dev_err(), not the USB
device.  Fix up the places where I got this wrong.

Reported-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
CC: Jesper Juhl <jj@chaosbits.net>
CC: JJ Ding <dgdunix@gmail.com>
CC: Edwin van Vliet <edwin@cheatah.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>