reactor: Fix indentation in reactor::open_file_dma
reactor: Fix indentation in reactor::open_file_dma

Just a passing cleanup while editing this area.

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

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