staging: unisys: visorbus: device_responder add error handling

The function controlvm_respond returns proper error handling, so now we
can propagate the error up and handle it appropriately.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>