[PARISC] Fix iounmap compile warning

iounmap's argument needs to be both const and volatile, otherwise we'll
get warnings that we're discarding pointer qualifiers

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
diff --git a/include/asm-parisc/io.h b/include/asm-parisc/io.h
index b9eb245..c1963ce 100644
--- a/include/asm-parisc/io.h
+++ b/include/asm-parisc/io.h
@@ -134,7 +134,7 @@
 }
 #define ioremap_nocache(off, sz)	ioremap((off), (sz))
 
-extern void iounmap(void __iomem *addr);
+extern void iounmap(const volatile void __iomem *addr);
 
 static inline unsigned char __raw_readb(const volatile void __iomem *addr)
 {