drm/msm/dpu: add division of drm_display_mode's hskew parameter

Setting up the timing engine when the physical encoder has a split role
neglects dividing the drm_display_mode's hskew parameter. Let's fix this
since this must also be done in preparation for implementing YUV420 over
DP.

Fixes: 25fdd593

 ("drm/msm: Add SDM845 DPU support")
Signed-off-by: Paloma Arellano <quic_parellan@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/579605/
Link: https://lore.kernel.org/r/20240222194025.25329-3-quic_parellan@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>