sh: Don't perform an icbi on a P2 address

The legacy P2 area may not always be mapped (for example when using
PMB). So perform an icbi on an address that we know will always be
mapped.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/system.h

@@ -32,7 +32,7 @@
 #define mb()		__asm__ __volatile__ ("synco": : :"memory")
 #define rmb()		mb()
 #define wmb()		__asm__ __volatile__ ("synco": : :"memory")
-#define ctrl_barrier()	__icbi(0xa8000000)
+#define ctrl_barrier()	__icbi(PAGE_OFFSET)
 #define read_barrier_depends()	do { } while(0)
 #else
 #define mb()		__asm__ __volatile__ ("": : :"memory")