USB: xpad.c: remove err() usage

err() was a very old USB-specific macro that I thought had
gone away.  This patch removes it from being used in the
driver and uses dev_err() instead.

CC: Dmitry Torokhov <dmitry.torokhov@gmail.com>
CC: "Magnus Hörlin" <magnus@alefors.se>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Mauro Carvalho Chehab <mchehab@redhat.com>
CC: Chris Moeller <kode54@gmail.c>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>