gpio: samsung: silent build warning for EXYNOS5 SoCs

This patch fixes following warning:

drivers/gpio/gpio-samsung.c:450:32: warning: 'exynos_gpio_cfg' defined but not used [-Wunused-variable]
drivers/gpio/gpio-samsung.c:2450:33: warning: 'exynos5_gpios_1' defined but not used [-Wunused-variable]
drivers/gpio/gpio-samsung.c:2618:33: warning: 'exynos5_gpios_2' defined but not used [-Wunused-variable]
drivers/gpio/gpio-samsung.c:2679:33: warning: 'exynos5_gpios_3' defined but not used [-Wunused-variable]
drivers/gpio/gpio-samsung.c:2715:33: warning: 'exynos5_gpios_4' defined but not used [-Wunused-variable]

Because current gpio-samsung is valid only on EXYNOS5250.

Cc: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>