staging: comedi: aio_iiro_16: read intial state of the digital outputs

The relay registers are readable. Read them during the attach to get
the initial state of the digital outputs.

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>