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/io_apic.h

@@ -1,5 +1,5 @@
-#ifndef ASM_X86__IO_APIC_H
-#define ASM_X86__IO_APIC_H
+#ifndef _ASM_X86_IO_APIC_H
+#define _ASM_X86_IO_APIC_H
 
 #include <linux/types.h>
 #include <asm/mpspec.h>
@@ -201,4 +201,4 @@ static inline int probe_nr_irqs(void)
 }
 #endif
 
-#endif /* ASM_X86__IO_APIC_H */
+#endif /* _ASM_X86_IO_APIC_H */