x86: Fix ASM_X86__ header guards

Change header guards named "ASM_X86__*" to "_ASM_X86_*" since:

a. the double underscore is ugly and pointless.
b. no leading underscore violates namespace constraints.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/include/asm/agp.h b/arch/x86/include/asm/agp.h
index 3617fd4..9825cd6 100644
--- a/arch/x86/include/asm/agp.h
+++ b/arch/x86/include/asm/agp.h
@@ -1,5 +1,5 @@
-#ifndef ASM_X86__AGP_H
-#define ASM_X86__AGP_H
+#ifndef _ASM_X86_AGP_H
+#define _ASM_X86_AGP_H
 
 #include <asm/pgtable.h>
 #include <asm/cacheflush.h>
@@ -32,4 +32,4 @@
 #define free_gatt_pages(table, order)	\
 	free_pages((unsigned long)(table), (order))
 
-#endif /* ASM_X86__AGP_H */
+#endif /* _ASM_X86_AGP_H */