of: property: Don't retry device_link_add() upon failure

When of_link_to_phandle() was implemented initially, there was no way to
tell if device_link_add() was failing because the supplier device hasn't
been parsed yet, hasn't been added yet, the links were creating a cycle,
etc. Some of these were transient errors that'd go away at a later
point.

However, with the current set of improved checks, if device_link_add()
fails, it'll only be for permanent errors like cycles or out-of-memory
errors.

Also, with the addition of DL_FLAG_SYNC_STATE_ONLY flag [1] to device
links, all the valid dependency cycles due to "proxy" device links
(needed for correctness of sync_state() device callback) will never fail
device_link_add() due to cycles.

So, continuing to retry failing device links (by returning -EAGAIN) is
no longer useful. At worst, it prevents platforms from setting
fw_devlink=on (or better) because it prevents proper boot up. So, let's
not do that anymore.

[1] - https://lore.kernel.org/lkml/20191028220027.251605-1-saravanak@google.com/
Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/property.c

@@ -1074,7 +1074,7 @@ static int of_link_to_phandle(struct device *dev, struct device_node *sup_np,
 		return -EAGAIN;
 	}
 	if (!device_link_add(dev, sup_dev, dl_flags))
-		ret = -EAGAIN;
+		ret = -EINVAL;
 	put_device(sup_dev);
 	return ret;
 }