clocksource: make CLOCKSOURCE_MASK bullet-proof

Signed-off-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/linux/clocksource.h

@@ -103,7 +103,7 @@ struct clocksource {
 #define CLOCK_SOURCE_VALID_FOR_HRES		0x20
 
 /* simplify initialization of mask field */
-#define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
+#define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
 
 /**
  * clocksource_khz2mult - calculates mult from khz and shift