pinctrl: samsung: Make symbol 'exynos7885_pin_ctrl' static

The sparse tool complains as follows:

drivers/pinctrl/samsung/pinctrl-exynos-arm64.c:490:31: warning:
 symbol 'exynos7885_pin_ctrl' was not declared. Should it be static?

This symbol is not used outside of pinctrl-exynos-arm64.c, so marks
it static.

Fixes: b0ef7b1a

 ("pinctrl: samsung: Add Exynos7885 SoC specific data")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20211123083617.2366756-1-weiyongjun1@huawei.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>