Setting ds->num_ports to DSA_MAX_PORTS made DSA core allocate unnecessary
dsa_port's and call mt7530_port_disable for non-existent ports.
Set it to MT7530_NUM_PORTS to fix that, and dsa_is_user_port check in
port_enable/disable is no longer required.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: DENG Qingfang <dqfext@xxxxxxxxx>