dt-bindings: pinctrl: aspeed: Fix AST2500 example errors

The schema examples are now validated against the schema itself. The
AST2500 pinctrl schema has a couple of errors:

Documentation/devicetree/bindings/pinctrl/aspeed,ast2500-pinctrl.example.dt.yaml: \
example-0: $nodename:0: 'example-0' does not match '^(bus|soc|axi|ahb|apb)(@[0-9a-f]+)?$'
Documentation/devicetree/bindings/pinctrl/aspeed,ast2500-pinctrl.example.dt.yaml: \
pinctrl: aspeed,external-nodes: [[1, 2]] is too short

Fixes: 0a617de1 ("dt-bindings: pinctrl: aspeed: Convert AST2500 bindings to json-schema")
Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Joel Stanley <joel@jms.id.au>
Cc: linux-aspeed@lists.ozlabs.org
Cc: linux-gpio@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Rob Herring <robh@kernel.org>