drm/msm/dpu: use defined symbol for sc8280xp's maxwidth

Use defined name DEFAULT_DPU_OUTPUT_LINE_WIDTH instead of open coding
the value.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/530866/
Link: https://lore.kernel.org/r/20230404130622.509628-30-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>