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>

arch/x86/include/asm/ipi.h

@@ -1,5 +1,5 @@
-#ifndef ASM_X86__IPI_H
-#define ASM_X86__IPI_H
+#ifndef _ASM_X86_IPI_H
+#define _ASM_X86_IPI_H
 
 /*
  * Copyright 2004 James Cleverdon, IBM.
@@ -135,4 +135,4 @@ static inline void send_IPI_mask_sequence(cpumask_t mask, int vector)
 	local_irq_restore(flags);
 }
 
-#endif /* ASM_X86__IPI_H */
+#endif /* _ASM_X86_IPI_H */