perf top: Fix zero or negative refresh delay

If perf top is executed with a zero value for the refresh rate,
we get a division by zero exception while computing samples_per_sec.

Also a zero refresh rate is not possible, neither do we want to
accept negative values.

[ Impact: fix division by zero in perf top ]

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1244223061-5399-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/perf_counter/builtin-top.c

@@ -693,6 +693,9 @@ int cmd_top(int argc, const char **argv, const char *prefix)
 		event_id[0] = 0;
 	}
 
+	if (delay_secs < 1)
+		delay_secs = 1;
+
 	for (counter = 0; counter < nr_counters; counter++) {
 		if (event_count[counter])
 			continue;