powerpc/4xx/cpm: delete unneeded test before of_node_put

Simplify the error path to avoid calling of_node_put when it is not needed.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>