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/intel_arch_perfmon.h b/arch/x86/include/asm/intel_arch_perfmon.h
index 07c03c6..fa0fd06 100644
--- a/arch/x86/include/asm/intel_arch_perfmon.h
+++ b/arch/x86/include/asm/intel_arch_perfmon.h
@@ -1,5 +1,5 @@
-#ifndef ASM_X86__INTEL_ARCH_PERFMON_H
-#define ASM_X86__INTEL_ARCH_PERFMON_H
+#ifndef _ASM_X86_INTEL_ARCH_PERFMON_H
+#define _ASM_X86_INTEL_ARCH_PERFMON_H
 
 #define MSR_ARCH_PERFMON_PERFCTR0		0xc1
 #define MSR_ARCH_PERFMON_PERFCTR1		0xc2
@@ -28,4 +28,4 @@
 	unsigned int full;
 };
 
-#endif /* ASM_X86__INTEL_ARCH_PERFMON_H */
+#endif /* _ASM_X86_INTEL_ARCH_PERFMON_H */