pinctrl: mscc: Fix multiple definition error

With gcc-11 we get a multiple errors here as the declarations for
mscc_pinctrl_ops and mscc_gpio_ops are missing an extern.

CC: Gregory CLEMENT <gregory.clement@bootlin.com>
Cc: Lars Povlsen <lars.povlsen@microchip.com>
Cc: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>