staging: comedi: dt2814: convert a printk(KERN_ERR into a dev_err()

Convert this printk message into a dev_dev().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>