cifsd: fix a IS_ERR() vs NULL bug

The smb_direct_alloc_sendmsg() function never returns NULL, it only
returns error pointers so the check needs to be updated.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifsd/transport_rdma.c

@@ -997,8 +997,8 @@ static int smb_direct_create_header(struct smb_direct_transport *t,
 	int ret;
 
 	sendmsg = smb_direct_alloc_sendmsg(t);
-	if (!sendmsg)
-		return -ENOMEM;
+	if (IS_ERR(sendmsg))
+		return PTR_ERR(sendmsg);
 
 	/* Fill in the packet header */
 	packet = (struct smb_direct_data_transfer *)sendmsg->packet;