PM / Domains: Correct unit address in power-controller example

In example 2 of the generic PM domains DT bindings, the unit address of
the device node representing the child power controller doesn't match
its "reg" property. Correct it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>