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/amd_iommu.h b/arch/x86/include/asm/amd_iommu.h
index 041d0db..f712344 100644
--- a/arch/x86/include/asm/amd_iommu.h
+++ b/arch/x86/include/asm/amd_iommu.h
@@ -17,8 +17,8 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  */
 
-#ifndef ASM_X86__AMD_IOMMU_H
-#define ASM_X86__AMD_IOMMU_H
+#ifndef _ASM_X86_AMD_IOMMU_H
+#define _ASM_X86_AMD_IOMMU_H
 
 #include <linux/irqreturn.h>
 
@@ -32,4 +32,4 @@
 static inline void amd_iommu_detect(void) { }
 #endif
 
-#endif /* ASM_X86__AMD_IOMMU_H */
+#endif /* _ASM_X86_AMD_IOMMU_H */