x86: Use "do { } while(0)" for empty lock_cmos()/unlock_cmos() macros

gcc noticed (when using -Wempty-body) that our use of
lock_cmos() and unlock_cmos() in
arch/x86/include/asm/mach_traps.h is potentially problematic :

  arch/x86/include/asm/mach_traps.h:32:15: warning: suggest braces around empty body in an ¡else¢ statement [-Wempty-body]
  arch/x86/include/asm/mach_traps.h:40:16: warning: suggest braces around empty body in an ¡else¢ statement [-Wempty-body]

Let's just use the standard 'do {} while (0)' solution. That
shuts up gcc and also prevents future problems if the macros
should end up being used in a similar situation elsewhere.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1112180103130.21784@swampdragon.chaosbits.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/mc146818rtc.h

@@ -81,8 +81,8 @@ static inline unsigned char current_lock_cmos_reg(void)
 #else
 #define lock_cmos_prefix(reg) do {} while (0)
 #define lock_cmos_suffix(reg) do {} while (0)
-#define lock_cmos(reg)
-#define unlock_cmos()
+#define lock_cmos(reg) do { } while (0)
+#define unlock_cmos() do { } while (0)
 #define do_i_have_lock_cmos() 0
 #define current_lock_cmos_reg() 0
 #endif