drm/msm/dpu: drop core_clk_rate overrides from _dpu_core_perf_calc_crtc

core_clk_rate override is handled in _dpu_core_perf_get_core_clk_rate().
Drop imperfect duplicating code from _dpu_core_perf_calc_crtc().

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/636070/
Link: https://lore.kernel.org/r/20250209-dpu-perf-rework-v5-7-87e936cf3004@linaro.org