coll/sm: fix minor memory leak

this is a backport of commit open-mpi/ompi@5d44a30111e730c1a6a9aef19548b87e704316de in master
In a first-order review, I don't see module->cm_bootstrap_meta being set to NULL in the constructor.

Without that, how can you know it's safe to OBJ_RELEASE c->sm_bootstream_beta?