dt-bindings: bus: Drop empty compatible string in example

In preparation to add generic checks of compatible strings, drop
the compatible as '...' is not a valid compatible string.

Cc: Maxime Ripard <[e-mail]>
Cc: Chen-Yu Tsai <[e-mail]>
Cc: [e-mail]
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/bus/allwinner,sun8i-a23-rsb.yaml

···
         #size-cells = <0>;
 
         pmic@3e3 {
-            compatible = "...";
             reg = <0x3e3>;
 
             /* ... */