coll/sm: fix minor memory leak

this is a backport of commit open-mpi/ompi@5d44a30111e730c1a6a9aef19548b87e704316de in master
c is *not* an object but is malloc'ed in ompi_coll_sm_lazy_enable(...)

sm_bootstrap_meta will be initialized in bootstrap_comm (invoked from ompi_coll_sm_lazy_enable), unless bootstrap_comm fails.
but even this case is correctly handled by ompi_coll_sm_lazy_enable.

also, if c->sm_bootstrap_meta were not a vaild pointer, mca_common_sm_fini would have crashed first with a glory SIGSEGV