nds32: Fix io.h warning message about readb

It is caused from asm/io.h declare different input type.

Signed-off-by: rick <rick@andestech.com>

arch/nds32/include/asm/io.h

@@ -125,26 +125,26 @@ extern void __raw_readsl(unsigned int addr, void *data, int longlen);
 #define __iormb()	dmb()
 #define __iowmb()	dmb()
 
-static inline void writeb(unsigned char val, unsigned char *addr)
+static inline void writeb(u8 val, volatile void __iomem *addr)
 {
 	__iowmb();
 	__arch_putb(val, addr);
 }
 
-static inline void writew(unsigned short val, unsigned short *addr)
+static inline void writew(u16 val, volatile void __iomem *addr)
 {
 	__iowmb();
 	__arch_putw(val, addr);
 
 }
 
-static inline void writel(unsigned int val, unsigned int *addr)
+static inline void writel(u32 val, volatile void __iomem *addr)
 {
 	__iowmb();
 	__arch_putl(val, addr);
 }
 
-static inline unsigned char readb(unsigned char *addr)
+static inline u8 readb(const volatile void __iomem *addr)
 {
 	u8	val;
 
@@ -153,7 +153,7 @@ static inline unsigned char readb(unsigned char *addr)
 	return val;
 }
 
-static inline unsigned short readw(unsigned short *addr)
+static inline u16 readw(const volatile void __iomem *addr)
 {
 	u16	val;
 
@@ -162,7 +162,7 @@ static inline unsigned short readw(unsigned short *addr)
 	return val;
 }
 
-static inline unsigned int readl(unsigned int *addr)
+static inline u32 readl(const volatile void __iomem *addr)
 {
 	u32	val;