staging: comedi: adl_pci9118: remove 'valid' from private data

This member of the private data is set only used during the (*detach)
to check if the board can be reset. The pci9118_reset() function just
needs a valid dev->iobase. Use that instead.

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>