drm/panel: simple: Add 50Hz mode for sharp,ls020b1dd01d

Add a perfect 50.00 Hz frame rate mode to the list of available modes
for the Sharp LS020B1DD01D panel.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200811002240.55194-6-paul@crapouillou.net