powerpc/powernv: fix missing of_node_put in uv_init()

of_find_compatible_node() returns 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/20220407090043.2491854-1-lv.ruyi@zte.com.cn