PM / OPP: Fix incorrect comments

Some comments were just copy/pasted from other sections and don't match
to the routines they were added for. Fix them.

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>