staging: comedi: rti800: cleanup dev->board_name usage

The comedi core initializes the dev->board_name before calling the
driver (*attach) function. There is not reason to reinitialize it
in the driver.

Use the dev->board_name when doing the request_{region,irq}() instead
of the open-coded string.

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>