staging: unisys: return meaningful error for visorchipset_init()

The other error paths return meaningful error codes, except for the one
when registering a device, which just returned -1. Let's return ENODEV
when it fails to register instead.

Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>