staging: unisys: visorbus: controlvm_respond_physdev_changestate add error handling

Propagate the error up the stack instead of ignoring it.

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>