staging: comedi: das1800: tidy up das1800_probe()

Refactor das1800_probe() to return an errno instead of the boardinfo
pointer.

Add the board 'id' to the boardinfo to tidy up this function to clarify
the sanity check when the user provided a board name when trying to
attach to the driver.

Currently when this function probes for a boardinfo based on the board
id it returns the wrong boardinfo for the "st-da" and "hr-da" types.
This causes the analog input subdevice for those boards to not be
available. Fix the probe so that a proper boardinfo is used.
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>