dev_pm_genpd_set_performance_state() will be required to call
dev_pm_opp_xlate_performance_state() going forward to translate from
performance state of a sub-domain to performance state of its master.
And dev_pm_opp_xlate_performance_state() needs pointers to the OPP
tables of both genpd and its master.

Lets fetch and save them while the OPP tables are added. Fetching the
OPP tables should never fail as we just added the OPP tables and so add
a WARN_ON() for such a bug instead of full error paths.
Tested-by: NRajendra Nayak <rnayak@codeaurora.org>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>