powerpc/xics: fix refcount leak in icp_opal_init()

The of_find_compatible_node() function returns a node pointer with
refcount incremented, use of_node_put() on it when done.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220402013419.2410298-1-lv.ruyi@zte.com.cn