x86: include proper prototypes for rodata_test

extern should not appear in C files.  Also, the definitions
do not match the prototype currently, not sure what way you
want to go with this, I've switched the prototype to return
int, but I can see going to the void return as well.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index b59fc23..a4a9ccc 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -45,6 +45,7 @@
 #include <asm/sections.h>
 #include <asm/kdebug.h>
 #include <asm/numa.h>
+#include <asm/cacheflush.h>
 
 const struct dma_mapping_ops *dma_ops;
 EXPORT_SYMBOL(dma_ops);