[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/init.c b/arch/s390/oprofile/init.c
index c63d7e5..5995e9b 100644
--- a/arch/s390/oprofile/init.c
+++ b/arch/s390/oprofile/init.c
@@ -145,15 +145,11 @@
 	 * create hwsampler files only if hwsampler_setup() succeeds.
 	 */
 	oprofile_min_interval = hwsampler_query_min_interval();
-	if (oprofile_min_interval < 0) {
-		oprofile_min_interval = 0;
+	if (oprofile_min_interval == 0)
 		return -ENODEV;
-	}
 	oprofile_max_interval = hwsampler_query_max_interval();
-	if (oprofile_max_interval < 0) {
-		oprofile_max_interval = 0;
+	if (oprofile_max_interval == 0)
 		return -ENODEV;
-	}
 
 	if (oprofile_timer_init(ops))
 		return -ENODEV;