dt-bindings: pinctrl: aspeed: Strip unnecessary quotes

Rob pointed out that we didn't need the noise of the quotes in a
separate review[1], so strip them out for consistency and avoid setting
a bad example.

[1] https://lists.ozlabs.org/pipermail/linux-aspeed/2019-July/002009.html



Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20190712061721.26645-1-andrew@aj.id.au


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