staging: unisys: use error codes

we were just returning -1 to the calling function which was again
returning that if the module failed to load. Now we are returning the
actual error codes.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>