mlxsw: spectrum_switchdev: Rename MIDs list

Currently, the list which stores the MDB entries for a given bridge
instance is called 'mids_list'.

This name is not accurate as a MID entry stores a bitmap of ports to
which a packet needs to be replicated and a MDB entry stores the mapping
from {MAC, FID} to PGT index (MID)

Rename it to 'mdb_list'.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>