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>

Documentation/devicetree/bindings/display/panel/toshiba,lt089ac29000.txt

 Toshiba 8.9" WXGA (1280x768) TFT LCD panel
 
 Required properties:
-- compatible: should be "toshiba,lt089ac29000.txt"
+- compatible: should be "toshiba,lt089ac29000"
 - power-supply: as specified in the base binding
 
 This binding is compatible with the simple-panel binding, which is specified