utils: i_filter: rename "format" variable
utils: i_filter: rename "format" variable

The format variable hides the format function, which we'll soon want to use
here. Rename the format variable to unhide the function.

scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla