pinctrl: samsung: staticize fsd_pin_ctrl

struct fsd_pin_ctrl is not used outside of the file, so it can be made
static.  This fixes sparse warning:

  drivers/pinctrl/samsung/pinctrl-exynos-arm64.c:773:31: sparse:
    symbol 'fsd_pin_ctrl' was not declared. Should it be static?

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 0d1b662c ("pinctrl: samsung: add FSD SoC specific data")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Link: https://lore.kernel.org/r/20220331194526.52444-1-krzysztof.kozlowski@linaro.org