dt-bindings: pinctrl: aspeed: Update gfx node in example

The example needs updating to match the to be added yaml bindings for
the gfx node.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220304000311.970267-2-joel@jms.id.au


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>