perf, x86: Use weight instead of cmask in for_each_event_constraint()

There may exist constraints with a cmask set to zero. In this case
for_each_event_constraint() will not work properly. Now weight is used
instead of the cmask for loop exit detection. Weight is always a value
other than zero since the default contains the HWEIGHT from the
counter mask and in other cases a value of zero does not fit too.

This is in preparation of ibs event constraints that wont have a
cmask.

Signed-off-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1271190201-25705-7-git-send-email-robert.richter@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/perf_event.c

@@ -170,7 +170,7 @@ struct cpu_hw_events {
 	EVENT_CONSTRAINT(0, 0, 0)
 
 #define for_each_event_constraint(e, c)	\
-	for ((e) = (c); (e)->cmask; (e)++)
+	for ((e) = (c); (e)->weight; (e)++)
 
 union perf_capabilities {
 	struct {