drm/bridge: tc358767: don't fixup mode sync polarity

There is no need to enforce a specific sync signal polarity on the
DPI interface, as we can simply tell the TC358767 which polarities
it should expect on the input interface.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Marek Vasut <marex@denx.de>
Tested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220706132812.2171250-1-l.stach@pengutronix.de