pinctrl: pinctrl-microchip-sgpio: Mark some symbols with static keyword

pinctrl: pinctrl-microchip-sgpio: Mark some symbols with static keyword

Fix the following sparse warnings:

drivers/pinctrl/pinctrl-microchip-sgpio.c:63:31: warning: symbol 'properties_luton' was not declared. Should it be static?
drivers/pinctrl/pinctrl-microchip-sgpio.c:68:31: warning: symbol 'properties_ocelot' was not declared. Should it be static?
drivers/pinctrl/pinctrl-microchip-sgpio.c:73:31: warning: symbol 'properties_sparx5' was not declared. Should it be static?

Signed-off-by: Zou Wei <zou_wei@huawei.com>
Link: https://lore.kernel.org/r/1606218173-3722-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>