drm/msm/dp: inline dp_power_clk_set_rate()

Inline the dp_power_clk_set_rate() function, replacing it with the call
to msm_dss_enable_clk().

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/474719/
Link: https://lore.kernel.org/r/20220217055529.499829-5-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>