pf: remove pointless NULL check

pfi_kkif_attach() always returns non-NULL, and we dereference the
pointer before we check it, so that's pointless.

Reported by:	Coverity (CID 1007345)
MFC after:	1 week
Sponsored by:	Rubicon Communications, LLC ("Netgate")

(cherry picked from commit ed6287c1)

sys/netpfil/pf/pf_if.c

@@ -549,8 +549,7 @@ pfi_dynaddr_setup(struct pf_addr_wrap *aw, sa_family_t af)
 		pfr_detach_table(dyn->pfid_kt);
 	if (ruleset != NULL)
 		pf_remove_if_empty_kruleset(ruleset);
-	if (dyn->pfid_kif != NULL)
-		pfi_kkif_unref(dyn->pfid_kif);
+	pfi_kkif_unref(dyn->pfid_kif);
 	free(dyn, PFI_MTYPE);
 
 	return (rv);