ARM: s3c64xx: include header to fix -Wmissing-prototypes

Include the spi-s3c64xx.h header to fix W=1 build warning:

    arch/arm/mach-s3c64xx/setup-spi.c:11:5: warning:
        no previous prototype for 's3c64xx_spi0_cfg_gpio' [-Wmissing-prototypes]
       11 | int s3c64xx_spi0_cfg_gpio(void)
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Tomasz Figa <tomasz.figa@gmail.com>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>

arch/arm/mach-s3c64xx/setup-spi.c

@@ -4,6 +4,7 @@
 //		http://www.samsung.com/
 
 #include <linux/gpio.h>
+#include <linux/platform_data/spi-s3c64xx.h>
 #include <plat/gpio-cfg.h>
 #include <mach/gpio-samsung.h>