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/pgtable-2level.h b/arch/x86/include/asm/pgtable-2level.h
index 8176208..b17edfd 100644
--- a/arch/x86/include/asm/pgtable-2level.h
+++ b/arch/x86/include/asm/pgtable-2level.h
@@ -1,5 +1,5 @@
-#ifndef ASM_X86__PGTABLE_2LEVEL_H
-#define ASM_X86__PGTABLE_2LEVEL_H
+#ifndef _ASM_X86_PGTABLE_2LEVEL_H
+#define _ASM_X86_PGTABLE_2LEVEL_H
 
 #define pte_ERROR(e) \
 	printk("%s:%d: bad pte %08lx.\n", __FILE__, __LINE__, (e).pte_low)
@@ -76,4 +76,4 @@
 #define __pte_to_swp_entry(pte)		((swp_entry_t) { (pte).pte_low })
 #define __swp_entry_to_pte(x)		((pte_t) { .pte = (x).val })
 
-#endif /* ASM_X86__PGTABLE_2LEVEL_H */
+#endif /* _ASM_X86_PGTABLE_2LEVEL_H */