powerpc/85xx: Add missing of_node_put() in sgy_cst1000

In gpio_halt_probe(), of_find_matching_node() will return a node
pointer with refcount incremented. The reference should be dropped with
of_node_put() in the failure path.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220617105011.4041123-1-windhl@126.com