bootstd: Add a way to set up a bootflow

Add a function to init a bootflow, to reduce code duplication.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/bootmeth-uclass.c

@@ -77,10 +77,7 @@ int bootmeth_get_bootflow(struct udevice *dev, struct bootflow *bflow)
 
 	if (!ops->read_bootflow)
 		return -ENOSYS;
-	memset(bflow, '\0', sizeof(*bflow));
-	bflow->dev = NULL;
-	bflow->method = dev;
-	bflow->state = BOOTFLOWST_BASE;
+	bootflow_init(bflow, NULL, dev);
 
 	return ops->read_bootflow(dev, bflow);
 }