staging: comedi: comedi_test: convert attach message to dev_info

Convert the 'attach' message from a printk to a dev_info.

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>