staging: unisys: cleanup rc -1 in create_visor_device()

Get rid of the rc = -1 initialization. Return a meaningful error on
failure in the function, or, the rc from a called function if it fails.

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