clk: renesas: cpg-mssr: Postpone call to pm_genpd_init()

All local setup of the generic_pm_domain structure should have been
completed before calling pm_genpd_init().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>