drbd: correctly handle failed crypto_alloc_hash

crypto_alloc_hash returns an ERR_PTR(), not NULL.

Also reset peer_integrity_tfm to NULL, to not call crypto_free_hash()
on an errno in the cleanup path.

Reported-by: Insu Yun <wuninsu@gmail.com>

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 0d74602..df45713 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -3681,7 +3681,8 @@
 		 */
 
 		peer_integrity_tfm = crypto_alloc_ahash(integrity_alg, 0, CRYPTO_ALG_ASYNC);
-		if (!peer_integrity_tfm) {
+		if (IS_ERR(peer_integrity_tfm)) {
+			peer_integrity_tfm = NULL;
 			drbd_err(connection, "peer data-integrity-alg %s not supported\n",
 				 integrity_alg);
 			goto disconnect;