staging: comedi: drivers: propogate errno from subdev_8255_init()

The initialization of the 8255 subdevice can fail due to the allocation
of the private data. Make sure all callers of subdev_8255_init() propogate
the errno.

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>