dt-bindings: arm: stm32: st,mlahb: Drop spurious "reg" property from example

"reg" is not documented nor used for st,mlahb, so drop it from the
example to fix the warning:

Documentation/devicetree/bindings/arm/stm32/st,mlahb.example.dtb: ahb@38000000: Unevaluated properties are not allowed ('reg' was unexpected)
        from schema $id: http://devicetree.org/schemas/arm/stm32/st,mlahb.yaml#

Since "reg" is dropped, the unit-address must be as well.
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240523154208.2457864-1-robh@kernel.orgSigned-off-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/arm/stm32/st,mlahb.yaml

@@ -54,11 +54,10 @@ unevaluatedProperties: false
 
 examples:
   - |
-    mlahb: ahb@38000000 {
+    ahb {
       compatible = "st,mlahb", "simple-bus";
       #address-cells = <1>;
       #size-cells = <1>;
-      reg = <0x10000000 0x40000>;
       ranges;
       dma-ranges = <0x00000000 0x38000000 0x10000>,
                    <0x10000000 0x10000000 0x60000>,