net: ethernet: ti: am65-cpsw: fix port_np reference counting

net: ethernet: ti: am65-cpsw: fix port_np reference counting

A reference to the device tree node is stored in a private struct, thus
the reference count has to be incremented. Also, decrement the count on
device removal and in the error path.

Fixes: 93a76530316a ("net: ethernet: ti: introduce am65x/j721e gigabit eth subsystem driver")
Signed-off-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250414083942.4015060-1-mwalle@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>