Deobfuscate cleanup path in clnt_dg_create(..)

Similar to r300836 and r301800, cl and cu will always be non-NULL as they're
allocated using the mem_alloc routines, which always use
`malloc(..., M_WAITOK)`.

Deobfuscating the cleanup path fixes a leak where if cl was NULL and
cu was not, cu would not be free'd, and also removes a duplicate test for
cl not being NULL.

MFC after: 1 week
Reported by: Coverity
CID: 1007033, 1007344
Sponsored by: EMC / Isilon Storage Division

sys/rpc/clnt_dg.c

@@ -313,11 +313,9 @@ clnt_dg_create(
 	cl->cl_netid = NULL;
 	return (cl);
 err2:
-	if (cl) {
 	mem_free(cl, sizeof (CLIENT));
-		if (cu)
 	mem_free(cu, sizeof (*cu));
-	}
+
 	return (NULL);
 }