repair: add missing ampersand
repair: add missing ampersand

This was a plain bug - ranges_opt is supposed to parse the option into
the vector "var", but took the vector by value.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

kjniemi/scylla,raphaelsc/scylla,scylladb/scylla,kjniemi/scylla,avikivity/scylla,duarten/scylla,raphaelsc/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,kjniemi/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,raphaelsc/scylla,duarten/scylla