test_objagg: Fix warning.

lib/test_objagg.c: In function ‘test_delta_action_item’:
./include/linux/printk.h:308:2: warning: ‘errmsg’ may be used uninitialized in this function [-Wmaybe-uninitialized]
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/test_objagg.c

@@ -769,6 +769,7 @@ static int test_delta_action_item(struct world *world,
 	if (err)
 		goto errout;
 
+	errmsg = NULL;
 	err = check_expect_stats(objagg, &action_item->expect_stats, &errmsg);
 	if (err) {
 		pr_err("Key %u: Stats: %s\n", action_item->key_id, errmsg);