soc: amlogic: meson-ee-pwrc: propagate PD provider registration errors

of_genpd_add_provider_onecell() can return an error. Propagate the error
so the driver registration fails when of_genpd_add_provider_onecell()
did not work.

Fixes: eef3c2ba ("soc: amlogic: Add support for Everything-Else power domains controller")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>