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/string_64.h b/arch/x86/include/asm/string_64.h
index a2add11d..2afe164 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -1,5 +1,5 @@
-#ifndef ASM_X86__STRING_64_H
-#define ASM_X86__STRING_64_H
+#ifndef _ASM_X86_STRING_64_H
+#define _ASM_X86_STRING_64_H
 
 #ifdef __KERNEL__
 
@@ -57,4 +57,4 @@
 
 #endif /* __KERNEL__ */
 
-#endif /* ASM_X86__STRING_64_H */
+#endif /* _ASM_X86_STRING_64_H */