V4L/DVB (4311): Fix possible dvb-pll oops

Supplying a NULL i2c adapter to dvb_pll_attach is allowed, for example with
mt352 demods. However, the pll i2c probe will segfault because it does not
check for this.
Signed-off-by: Andrew de Quincey <adq_dvb@lidskialf.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/dvb/frontends/dvb-pll.c

@@ -619,14 +619,16 @@ int dvb_pll_attach(struct dvb_frontend *fe, int pll_addr, struct i2c_adapter *i2
 	struct dvb_pll_priv *priv = NULL;
 	int ret;
 
-	if (fe->ops.i2c_gate_ctrl)
-		fe->ops.i2c_gate_ctrl(fe, 1);
-
-	ret = i2c_transfer (i2c, msg, 2);
-	if (ret != 2)
-		return -1;
-	if (fe->ops.i2c_gate_ctrl)
-		     fe->ops.i2c_gate_ctrl(fe, 0);
+	if (i2c != NULL) {
+		if (fe->ops.i2c_gate_ctrl)
+			fe->ops.i2c_gate_ctrl(fe, 1);
+
+		ret = i2c_transfer (i2c, msg, 2);
+		if (ret != 2)
+			return -1;
+		if (fe->ops.i2c_gate_ctrl)
+			     fe->ops.i2c_gate_ctrl(fe, 0);
+	}
 
 	priv = kzalloc(sizeof(struct dvb_pll_priv), GFP_KERNEL);
 	if (priv == NULL)