net: dsa: sja1105: Unset port from forwarding mask unconditionally on fdb_del

This is a cosmetic patch that simplifies the code by removing a
redundant check. A logical AND-with-zero performed on a zero is still
zero.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>