powerpc: dts: turris1x.dts: Fix labels in DSA cpu port nodes

DSA cpu port node has to be marked with "cpu" label.
So fix it for both cpu port nodes.

Fixes: 54c15ec3

 ("powerpc: dts: Add DTS file for CZ.NIC Turris 1.x routers")
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220827131538.14577-1-pali@kernel.org