[S390] oprofile: fix min/max interval query checks

oprofile_min_interval and oprofile_max_interval are unsigned, checking
for negative values doesn't work. Change hwsampler_query_min_interval
and hwsampler_query_max_interval to return an unsigned long and
check for a zero value instead.

Reported-by: Nicolas Kaiser <nikai@nikai.net>
Acked-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/oprofile/hwsampler.c b/arch/s390/oprofile/hwsampler.c
index 4952872..33cbd37 100644
--- a/arch/s390/oprofile/hwsampler.c
+++ b/arch/s390/oprofile/hwsampler.c
@@ -1021,20 +1021,14 @@
 	return rc;
 }
 
-long hwsampler_query_min_interval(void)
+unsigned long hwsampler_query_min_interval(void)
 {
-	if (min_sampler_rate)
-		return min_sampler_rate;
-	else
-		return -EINVAL;
+	return min_sampler_rate;
 }
 
-long hwsampler_query_max_interval(void)
+unsigned long hwsampler_query_max_interval(void)
 {
-	if (max_sampler_rate)
-		return max_sampler_rate;
-	else
-		return -EINVAL;
+	return max_sampler_rate;
 }
 
 unsigned long hwsampler_get_sample_overflow_count(unsigned int cpu)