USB: iforce: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>