database: Add non-const version of get_row_cache
database: Add non-const version of get_row_cache

We need this to invalidate row cache of a column family.

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