doc: queue: fix @func
doc: queue: fix @func

Resolves following warning:
include/seastar/core/queue.hh:57: warning: Found unknown command '\func'

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

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