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/dma.h b/arch/x86/include/asm/dma.h
index c9f7a4e..ca1098a 100644
--- a/arch/x86/include/asm/dma.h
+++ b/arch/x86/include/asm/dma.h
@@ -5,8 +5,8 @@
  * and John Boyd, Nov. 1992.
  */
 
-#ifndef ASM_X86__DMA_H
-#define ASM_X86__DMA_H
+#ifndef _ASM_X86_DMA_H
+#define _ASM_X86_DMA_H
 
 #include <linux/spinlock.h>	/* And spinlocks */
 #include <asm/io.h>		/* need byte IO */
@@ -315,4 +315,4 @@
 #define isa_dma_bridge_buggy	(0)
 #endif
 
-#endif /* ASM_X86__DMA_H */
+#endif /* _ASM_X86_DMA_H */