staging: comedi: amplc_pci230: standardize error handling of subdev_8255_init()

The subdev_8255_init() call returns 0 for success of a negative errno for failure.
For aesthetics, change the error test in this driver from (rc < 0) to simply (rc)
to follow the style of the other users of this function.

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>