mlxsw: spectrum_acl: Fix SRC_SYS_PORT element size

Fix the size of the SRC_SYS_PORT element to be 16.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>