greybus: interface: fix svc-resource error messages

The interface svc-resource helper are used to enable as well as disable
the corresponding SVC resources so make sure the error messages reflect
that.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>