libsmartcols: fix memory leak in filter reset

libsmartcols: fix memory leak in filter reset

When parsing fails, filter params allocated during parsing but never
incorporated into the AST tree remain on the fltr->params list. The
reset_filter() only freed the tree via fltr->root, leaving orphaned
params leaked.

Add filter_free_params() to drain any remaining params from the list
during filter reset.

Addresses: https://github.com/util-linux/util-linux/pull/4430
Signed-off-by: Karel Zak <kzak@redhat.com>