Revert "serial/sunsu: add missing of_node_put()"

This reverts commit 20d8e861.

As David Miller points out, it's wrong.

Reported-by: David Miller <davem@davemloft.net>
Cc: Yangtao Li <tiny.windzz@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>