media: stv6111: return NULL instead of plain integer

Fixes:
  stv6111.c:665:24: warning: Using plain integer as NULL pointer
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/dvb-frontends/stv6111.c

@@ -669,7 +669,7 @@ struct dvb_frontend *stv6111_attach(struct dvb_frontend *fe,
 		fe->ops.i2c_gate_ctrl(fe, 0);
 	if (stat < 0) {
 		kfree(state);
-		return 0;
+		return NULL;
 	}
 	fe->tuner_priv = state;
 	return fe;