IB/mlx5: Check the correct variable in error handling code

The code accidentally checks "event_sub" instead of "event_sub->eventfd".

Fixes: 75973853 ("IB/mlx5: Enable subscription for device events over DEVX")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Link: https://lore.kernel.org/r/20190807123236.GA11452@mwandaSigned-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/devx.c

@@ -2026,7 +2026,7 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_DEVX_SUBSCRIBE_EVENT)(
 			event_sub->eventfd =
 				eventfd_ctx_fdget(redirect_fd);
 
-			if (IS_ERR(event_sub)) {
+			if (IS_ERR(event_sub->eventfd)) {
 				err = PTR_ERR(event_sub->eventfd);
 				event_sub->eventfd = NULL;
 				goto err;