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/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 8ec940b..8aeeb3f 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -1,5 +1,5 @@
-#ifndef ASM_X86__MMU_CONTEXT_H
-#define ASM_X86__MMU_CONTEXT_H
+#ifndef _ASM_X86_MMU_CONTEXT_H
+#define _ASM_X86_MMU_CONTEXT_H
 
 #include <asm/desc.h>
 #include <asm/atomic.h>
@@ -34,4 +34,4 @@
 } while (0);
 
 
-#endif /* ASM_X86__MMU_CONTEXT_H */
+#endif /* _ASM_X86_MMU_CONTEXT_H */