xtensa: xtfpga: Fix refcount leak bug in setup

In machine_setup(), of_find_compatible_node() will return a node
pointer with refcount incremented. We should use of_node_put() when
it is not used anymore.

Cc: stable@vger.kernel.org
Signed-off-by: Liang He <windhl@126.com>
Message-Id: <20220617115323.4046905-1-windhl@126.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>