dt-bindings: display: st,stm32-dsi: Fix panel node name in example

With 'unevaluatedProperties' support enabled, the st,stm32-dsi binding
has a new warning:

Documentation/devicetree/bindings/display/st,stm32-dsi.example.dt.yaml: dsi@5a000000: Unevaluated properties are not allowed ('panel-dsi@0' was unexpected)

The documented child node name is 'panel', so update the example.

Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/display/st,stm32-dsi.yaml

···
               };
         };
 
-        panel-dsi@0 {
+        panel@0 {
               compatible = "orisetech,otm8009a";
               reg = <0>;
               reset-gpios = <&gpioe 4 GPIO_ACTIVE_LOW>;
···
     };
 
 ...
-