pf: fix double free if pf_ioctl_addrule() fails

If pf_ioctl_addrule() returns an error it will have freed the rule
itself. There's no need for the caller to free it again.

PR: 274915
Reported by: Dave Cottlehuber <dch@FreeBSD.org>
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")