spi: s3c64xx: explicitly include <linux/io.h>

spi: s3c64xx: explicitly include <linux/io.h>

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.

Reviewed-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://lore.kernel.org/r/20240207120431.2766269-3-tudor.ambarus@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>