powerpc/85xx: Add missing of_node_get/put() in ge_imp3a_pci_assign_primary()

for_each_node_by_type() will automatically increase and decrease
the refcount during the iteration. However, there is a reference
escaped into global 'fsl_pci_primary' and we need to handle it.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220701140119.245435-1-windhl@126.com