pmdomain: core: Use genpd->opp_table to simplify error/remove path

While we add an OF-provider we may, based upon a specific condition, also
assign genpd->opp_table. Rather using the same specific condition in the
error/remove path, let's check genpd->opp_table instead as it makes the
code easier.

Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20250417142513.312939-4-ulf.hansson@linaro.org