USB: aiptek.c: remove dbg() usage

dbg() was a very old USB-specific macro that should no longer
be used. This patch removes it from being used in the driver
and uses dev_dbg() instead.

CC: 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>