[media] videobuf-dvb: avoid spurious ENOMEM when CONFIG_DVB_NET=n

videobuf_dvb_register_bus relies on dvb_net_init to set dvbnet->dvbdev
on success, but ever since commit fcc8e7d8c0e2 ("dvb_net: Simplify the
code if DVB NET is not defined"), ->dvbdev is left unset when
networking support is disabled. Therefore in such configurations
videobuf_dvb_register_bus always returns failure, tripping
little-tested error handling paths and preventing the device from
being initialized and used.

Now that dvb_net_init returns a nonzero value on error, we can use
that as a more reliable error indication. Do so.

Now your card be used with CONFIG_DVB_NET=n, and the kernel will pass
on a more useful error code describing what happened when
CONFIG_DVB_NET=y but dvb_net_init fails due to resource exhaustion.

Reported-by: David Fries <[e-mail]>
Signed-off-by: Jonathan Nieder <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/video/videobuf-dvb.c

···
 	}
 
 	/* register network adapter */
-	dvb_net_init(adapter, &dvb->net, &dvb->demux.dmx);
-	if (dvb->net.dvbdev == NULL) {
-		result = -ENOMEM;
+	result = dvb_net_init(adapter, &dvb->net, &dvb->demux.dmx);
+	if (result < 0) {
+		printk(KERN_WARNING "%s: dvb_net_init failed (errno = %d)\n",
+		       dvb->name, result);
 		goto fail_fe_conn;
 	}
 	return 0;