future: Replace a call to futurize_apply with futurize_invoke
future: Replace a call to futurize_apply with futurize_invoke

We were constructing a tuple just to call futurize_apply. Just call
futurize_invoke instead.

Signed-off-by: Rafael Ávila de Espíndola <1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>
Message-Id: <20200519213420.399905-1-1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>

syuu1228/seastar,avikivity/seastar,avikivity/seastar,scylladb/seastar,dreamsxin/seastar,syuu1228/seastar,syuu1228/seastar,avikivity/seastar,scylladb/seastar,cloudius-systems/seastar,cloudius-systems/seastar,cloudius-systems/seastar,dreamsxin/seastar,dreamsxin/seastar,scylladb/seastar