expo: Drop the render from expo_poll()

Within tests it is useful to be able to control rendering of the expo.
Drop the automatic call to expo_render() within expo_poll() and adjust
its callers to handle this instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/bootflow.c b/cmd/bootflow.c
index efac27a..55643a6 100644
--- a/cmd/bootflow.c
+++ b/cmd/bootflow.c
@@ -116,6 +116,9 @@
 		return log_msg_ret("bhs", ret);
 
 	do {
+		ret = expo_render(exp);
+		if (ret)
+			return log_msg_ret("bhr", ret);
 		ret = bootflow_menu_poll(exp, &bflow);
 	} while (ret == -EAGAIN);