of: of_node_get()/of_node_put() nodes held in phandle cache

The phandle cache contains struct device_node pointers.  The refcount
of the pointers was not incremented while in the cache, allowing use
after free error after kfree() of the node.  Add the proper increment
and decrement of the use count.

Fixes: 0b3ce78e ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")
Cc: stable@vger.kernel.org # v4.17+
Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>