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: Jaswinder Singh <jaswinder@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>