pinctrl: amlogic: Staticize some local structs

Sparse complains:

sparse warnings: (new ones prefixed by >>)
>> drivers/pinctrl/meson/pinctrl-amlogic-a4.c:126:24: sparse: sparse:
   symbol 'multi_mux_s7' was not declared. Should it be static?
>> drivers/pinctrl/meson/pinctrl-amlogic-a4.c:135:28: sparse: sparse:
   symbol 's7_priv_data' was not declared. Should it be static?
>> drivers/pinctrl/meson/pinctrl-amlogic-a4.c:140:24: sparse: sparse:
   symbol 'multi_mux_s6' was not declared. Should it be static?
>> drivers/pinctrl/meson/pinctrl-amlogic-a4.c:154:28: sparse: sparse:
   symbol 's6_priv_data' was not declared. Should it be static?

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506122145.wWAtKBoy-lkp@intel.com/


Cc: Xianwei Zhao <xianwei.zhao@amlogic.com>
Fixes: 1f8e5dfd ("pinctrl: meson: support amlogic S6/S7/S7D SoC")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/20250624-amlogic-a4-fix-v1-1-03f0856d10cb@linaro.org