nvme_disk: Request callbacks in libnvme are called with the qpair lock held.

Fixes #15880.

src/add-ons/kernel/drivers/disk/nvme/libnvme/nvme_request.c

@@ -67,7 +67,7 @@ static void nvme_request_cb_complete_child(void *child_arg,
 	if (parent->child_reqs == 0) {
 		if (parent->cb_fn)
 			parent->cb_fn(parent->cb_arg, &parent->parent_status);
-		nvme_request_free(parent);
+		nvme_request_free_locked(parent);
 	}
 }