driver: core: Improve documentation for fwnode_operations.add_links()

The add_links() ops shouldn't return on the first failed device link
add. It needs to continue trying to add device links to other suppliers
that are available. The documentation didn't explain WHY this behavior
is necessary. So, update the documentation with an example that explains
why this is necessary.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20191011191521.179614-3-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>