drm/msm/dp: "inline" dp_ctrl_set_clock_rate("ctrl_link")

"ctrl_link" is the clock from DP_CTRL_PM module. The result of setting
the rate for it would be a call to dev_pm_opp_set_rate(). Instead of
saving the rate inside struct dss_module_power, call the
devm_pm_opp_set_rate() directly.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/474712/
Link: https://lore.kernel.org/r/20220217055529.499829-3-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>