[MIPS] Add 'const' to readb and friends
    
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

---
diff --git a/include/asm-mips/io.h b/include/asm-mips/io.h
index a9fa125..05de7c1 100644
--- a/include/asm-mips/io.h
+++ b/include/asm-mips/io.h
@@ -342,7 +342,7 @@
 		BUG();							\
 }									\
 									\
-static inline type pfx##read##bwlq(volatile void __iomem *mem)		\
+static inline type pfx##read##bwlq(const volatile void __iomem *mem)	\
 {									\
 	volatile type *__mem;						\
 	type __val;							\