IB/srp: Fix return value check in srp_init_module()

In case of error, the function create_workqueue() returns NULL pointer
not ERR_PTR().  The IS_ERR() test in the return value check should be
replaced with NULL test.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/srp/ib_srp.c

@@ -3320,8 +3320,8 @@ static int __init srp_init_module(void)
 	}
 
 	srp_remove_wq = create_workqueue("srp_remove");
-	if (IS_ERR(srp_remove_wq)) {
-		ret = PTR_ERR(srp_remove_wq);
+	if (!srp_remove_wq) {
+		ret = -ENOMEM;
 		goto out;
 	}