soc: rockchip: power-domain: Handle errors from of_genpd_add_provider_onecell

It was a bit surprising that the device was reported to have probed just
fine, but the provider hadn't been registered.

So handle any errors when registering the provider and fail the probe
accordingly.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>