net dsa: qca8k: fix usages of device_get_named_child_node()

The documentation for device_get_named_child_node() mentions this
important point:

"
The caller is responsible for calling fwnode_handle_put() on the
returned fwnode pointer.
"

Add fwnode_handle_put() to avoid leaked references.

Fixes: 1e264f9d ("net: dsa: qca8k: add LEDs basic support")
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>