net: dsa: legacy: don't unmask port bitmaps

The legacy code does not unmask the cpu_port_mask and dsa_port_mask as
stated. But this is done on the error path and those masks won't be used
after that. So instead of fixing the bit operation, simply remove it.

Fixes: 83c0afae ("net: dsa: Add new binding implementation")
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>