[media] drivers/media/pci/saa7134/saa7134-dvb.c: Test if videobuf_dvb_get_frontend return NULL

Based on commit: e66131ce
Not testing videobuf_dvb_get_frontend output may cause OOPS if it return
NULL. This patch fixes this issue.
The semantic patch that found this issue is(http://coccinelle.lip6.fr/):
// <smpl>
@@
identifier i,a,b;
statement S, S2;
@@
i = videobuf_dvb_get_frontend(...);
... when != if (!i) S
* if (i->a.b)
S2
// </smpl>
Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/pci/saa7134/saa7134-dvb.c

@@ -607,6 +607,9 @@ static int configure_tda827x_fe(struct saa7134_dev *dev,
 	/* Get the first frontend */
 	fe0 = videobuf_dvb_get_frontend(&dev->frontends, 1);
 
+	if (!fe0)
+		return -EINVAL;
+
 	fe0->dvb.frontend = dvb_attach(tda10046_attach, cdec_conf, &dev->i2c_adap);
 	if (fe0->dvb.frontend) {
 		if (cdec_conf->i2c_gate)