ARM: exynos: Add missing declaration for gpio_direction_input

This patch adds missing declaration for gpio_direction_input
function, thereby helps in resolving compilation warnings.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

arch/arm/include/asm/arch-exynos/gpio.h

@@ -1504,6 +1504,7 @@ static const struct gpio_name_num_table exynos5420_gpio_table[] = {
 void gpio_cfg_pin(int gpio, int cfg);
 void gpio_set_pull(int gpio, int mode);
 void gpio_set_drv(int gpio, int mode);
+int gpio_direction_input(unsigned gpio);
 int gpio_direction_output(unsigned gpio, int value);
 int gpio_set_value(unsigned gpio, int value);
 int gpio_get_value(unsigned gpio);