drm/msm/dsi: improve/fix dsc pclk calculation

drm/msm/dsi: improve/fix dsc pclk calculation

[ Upstream commit 24436a540d16ca6a523b8e5441180001c31b6b35 ]

drm_mode_vrefresh() can introduce a large rounding error, avoid it.

Fixes: 7c9e4a554d4a ("drm/msm/dsi: Reduce pclk rate for compression")
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/618432/
Link: https://lore.kernel.org/r/20241007050157.26855-1-jonathan@marek.ca
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>