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/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
index edb3b4e..6d93508 100644
--- a/arch/x86/include/asm/pvclock-abi.h
+++ b/arch/x86/include/asm/pvclock-abi.h
@@ -1,5 +1,5 @@
-#ifndef ASM_X86__PVCLOCK_ABI_H
-#define ASM_X86__PVCLOCK_ABI_H
+#ifndef _ASM_X86_PVCLOCK_ABI_H
+#define _ASM_X86_PVCLOCK_ABI_H
 #ifndef __ASSEMBLY__
 
 /*
@@ -39,4 +39,4 @@
 } __attribute__((__packed__));
 
 #endif /* __ASSEMBLY__ */
-#endif /* ASM_X86__PVCLOCK_ABI_H */
+#endif /* _ASM_X86_PVCLOCK_ABI_H */