meson-gx-socinfo: make local function meson_gx_socinfo_init static

Fixes the following sparse warnings:

drivers/soc/amlogic/meson-gx-socinfo.c:100:12: warning:
 symbol 'meson_gx_socinfo_init' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>