db,view: fix waiting for a view building future
db,view: fix waiting for a view building future

The future was marked with a `FIXME: discarded future`, but there's really
no reason not to wait for it, and it was probably meant to be waited for
since its implementation.

avikivity/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla