USB: Staging: serqt_usb2: 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: Bill Pemberton <wfp5p@virginia.edu>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>