contrib/check-config.sh: fix IOSCHED_CFQ CFQ_GROUP_IOSCHED

These config options are removed by kernel commit f382fb0bcef4,
which made its way into kernel v5.0-rc1.

Make the check conditional.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

contrib/check-config.sh

@@ -283,8 +283,12 @@ else
 	netprio=CGROUP_NET_PRIO
 fi
 
+if [ "$kernelMajor" -lt 5 ]; then
+	check_flags IOSCHED_CFQ CFQ_GROUP_IOSCHED
+fi
+
 flags=(
-	BLK_CGROUP BLK_DEV_THROTTLING IOSCHED_CFQ CFQ_GROUP_IOSCHED
+	BLK_CGROUP BLK_DEV_THROTTLING
 	CGROUP_PERF
 	CGROUP_HUGETLB
 	NET_CLS_CGROUP $netprio