staging: comedi: s626: add final attach message

Add a simple dev_info() message after a successfull attach.
Change the final return to '0' to indicate success.

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>