drm/msm/dp: Inline dp_display_is_sink_count_zero()

drm/msm/dp: Inline dp_display_is_sink_count_zero()

This function is basically a one-liner when you ignore the debug
logging. Just inline the function and drop the log to simplify the code.

Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Vinod Polimera <quic_vpolimer@quicinc.com>
Cc: Kuogee Hsieh <quic_khsieh@quicinc.com>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/556066/
Link: https://lore.kernel.org/r/20230906181226.2198441-2-swboyd@chromium.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>