tests: do not try to 'flushbufs' after stopping a array

If the array is stopped, there is nothing to flush, and
blockdev can signal an error.

Signed-off-by: NeilBrown <neilb@suse.com>

tests/19raid6auto-repair

@@ -39,5 +39,3 @@ cmp -s -n $array_data_size_in_b $md0 /tmp/RandFile || { echo cmp failed ; exit 2
 
 mdadm -S $md0
 udevadm settle
-blockdev --flushbufs $md0 $devs; sync
-echo 3 > /proc/sys/vm/drop_caches

tests/19raid6repair

@@ -42,6 +42,6 @@ for failure in "$dev3 3 3 2" "$dev3 3 2 3" "$dev3 3 2 1" "$dev3 3 2 0" "$dev4 3
 
 	mdadm -S $md0
 	udevadm settle
-	blockdev --flushbufs $devs; sync
+	sync
 	echo 3 > /proc/sys/vm/drop_caches
 done

tests/19repair-does-not-destroy

@@ -26,4 +26,3 @@ cmp -s -n $array_data_size_in_b $md0 /tmp/RandFile || { echo should not mess up
 
 mdadm -S $md0
 udevadm settle
-blockdev --flushbufs $md0 $devs; sync