x86: traps.c replace #if CONFIG_X86_32 with #ifdef CONFIG_X86_32

Impact: cleanup, avoid warning on X86_64

Fixes this warning on X86_64:

  CC      arch/x86/kernel/traps.o
  arch/x86/kernel/traps.c:695:5: warning: "CONFIG_X86_32" is not defined
Signed-off-by: NJaswinder Singh <jaswinder@infradead.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/traps.c

@@ -691,7 +691,7 @@ void math_error(void __user *ip)
 
 	err = swd & ~cwd & 0x3f;
 
-#if CONFIG_X86_32
+#ifdef CONFIG_X86_32
 	if (!err)
 		return;
 #endif