nds32: Fix the unknown type u8 issue.

It broke the 'allmodconfig' build.
We need to include <linux/types.h> to make sure the type is defined
before using it.
Signed-off-by: NGreentime Hu <greentime@andestech.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>

arch/nds32/include/asm/io.h

@@ -4,6 +4,8 @@
 #ifndef __ASM_NDS32_IO_H
 #define __ASM_NDS32_IO_H
 
+#include <linux/types.h>
+
 extern void iounmap(volatile void __iomem *addr);
 #define __raw_writeb __raw_writeb
 static inline void __raw_writeb(u8 val, volatile void __iomem *addr)