staging: comedi: ni_mio_common: convert printk messages to dev_err

Where possible, convert the printk() messages in this file to dev_err().

Remove a couple commented out printk() messages.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>