drm/msm/dsi: remove extra call to dsi_get_pclk_rate()

drm/msm/dsi: remove extra call to dsi_get_pclk_rate()

In dsi_calc_clk_rate_v2() there is no need to call dsi_get_pclk_rate().
This function has just been called (from dsi_calc_pclk()) and its
result is stored at msm_host->pixel_clk_rate. Use this variable
directly.

Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/538272/
Link: https://lore.kernel.org/r/20230520200103.4019607-1-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>