[PATCH] highmem.h needs mm.h

From: David Mosberger <davidm@napali.hpl.hp.com>

highmem.h uses stuff like page_address(), but fails to include
<linux/mm.h>.

include/linux/highmem.h

@@ -3,6 +3,8 @@
 
 #include <linux/config.h>
 #include <linux/fs.h>
+#include <linux/mm.h>
+
 #include <asm/cacheflush.h>
 
 #ifdef CONFIG_HIGHMEM