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/gpio.h b/arch/x86/include/asm/gpio.h
index 497fb98..1c07aad 100644
--- a/arch/x86/include/asm/gpio.h
+++ b/arch/x86/include/asm/gpio.h
@@ -53,4 +53,4 @@
 
 #endif /* CONFIG_GPIOLIB */
 
-#endif /* ASM_X86__GPIO_H */
+#endif /* _ASM_X86_GPIO_H */