The driver uses readl() but does not include <linux/io.h>.

It is good practice to directly include all headers used, it avoids
implicit dependencies and spurious breakage if someone rearranges
headers and causes the implicit include to vanish.

Include the missing header.

Fixes: 230d42d422e7 ("spi: Add s3c64xx SPI Controller driver")
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
---
 drivers/spi/spi-s3c64xx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index 7f7eb8f742e4..c1cbc4780a3b 100644
--- a/drivers/spi/spi-s3c64xx.c
+++ b/drivers/spi/spi-s3c64xx.c
@@ -10,6 +10,7 @@
 #include <linux/clk.h>
 #include <linux/dma-mapping.h>
 #include <linux/dmaengine.h>
+#include <linux/io.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/spi/spi.h>
-- 
2.43.0.429.g432eaa2c6b-goog