ssa.c: Set default value to smdb_epoch field in ssa_access_member

The default epoch is DB_EPOCH_INVALID. It causes prdb computation for
new connected ACM (no matter whether real or "fake").

Signed-off-by: Sasha Kotchubievsky <sashakot@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>