pinctrl: falcon: mark pinctrl_falcon_init() as static

pinctrl: falcon: mark pinctrl_falcon_init() as static

Fix the following missing-prototypes build warning:

drivers/pinctrl/pinctrl-falcon.c:508:12: error: no previous prototype for 'pinctrl_falcon_init' [-Werror=missing-prototypes]
  508 | int __init pinctrl_falcon_init(void)
      |            ^~~~~~~~~~~~~~~~~~~

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://lore.kernel.org/OSBPR01MB167014AF54EF9818CB98C83BBC72A@OSBPR01MB1670.jpnprd01.prod.outlook.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>