PM / OPP: Remove useless TODO

This TODO doesn't make sense anymore as we have all the information in a
single OPP table. Remove it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>