V4L/DVB (5816): Cx88-blackbird: fix vidioc_g_tuner never ending list of tuners

v4l-info and other programs would loop indefinitely while querying the
tuners for cx88-blackbird cards.

The cause was that vidioc_g_tuner didn't return an error value for
qctrl->id != 0, making the application think there is a never ending
list of tuners...

This patch adds the same index check as done in vidioc_g_tuner() in
cx88-video.
Signed-off-by: Jelle Foks <jelle@foks.8m.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/cx88/cx88-blackbird.c

@@ -1034,6 +1034,8 @@ static int vidioc_g_tuner (struct file *file, void *priv,
 
 	if (unlikely(UNSET == core->tuner_type))
 		return -EINVAL;
+	if (0 != t->index)
+		return -EINVAL;
 
 	strcpy(t->name, "Television");
 	t->type       = V4L2_TUNER_ANALOG_TV;