PM / OPP: Relocate dev_pm_opp_set_sharing_cpus()

Move dev_pm_opp_set_sharing_cpus() towards the end of the file. This
is required for better readability after the next patch is applied,
which adds dev_pm_opp_get_sharing_cpus().

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>