drm/panel: simple: fix flags on RK043FN48H

DISPLAY_FLAGS_SYNC_POSEDGE is missing in the flags on the default
timings. When overriding the default mode with one described in the
device tree, the mode does not get acked because of this missing flag.
Moreover since the panel is driven by the positive edge it makes sense
to add it here.

Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Link: https://lore.kernel.org/r/20240205-ltdc_mp13-v1-4-072d24bf1b36@foss.st.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240205-ltdc_mp13-v1-4-072d24bf1b36@foss.st.com