drm/panel: boe-th101mb31ig002 : using drm_connector_helper_get_modes_fixed()

Use public functions( drm_connector_helper_get_modes_fixed()) to
get porch parameters.

Signed-off-by: Zhaoxiong Lv <lvzhaoxiong@huaqin.corp-partner.google.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240723062615.14796-3-lvzhaoxiong@huaqin.corp-partner.google.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240723062615.14796-3-lvzhaoxiong@huaqin.corp-partner.google.com