dt-bindings: display: panel: Fix compatible string for Toshiba LT089AC29000

The compatible string for this panel was specified as
toshiba,lt089ac29000.txt. I believe this is a mistake.

Fixes: 06e733e4 ("drm/panel: simple: add Toshiba LT089AC19000")
Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Acked-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Rob Herring <robh@kernel.org>