[media] em28xx: use v4l2_disable_ioctl() to disable ioctls VIDIOC_G_AUDIO and VIDIOC_S_AUDIO

Instead of checking the device type and returning -EINVAL inside the ioctl
functions, use v4l2_disable_ioctl() to disable the ioctls VIDIOC_G_AUDIO and
VIDIOC_S_AUDIO if the device doesn't support audio.
Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/usb/em28xx/em28xx-video.c

@@ -1130,9 +1130,6 @@ static int vidioc_g_audio(struct file *file, void *priv, struct v4l2_audio *a)
 	struct em28xx_fh   *fh    = priv;
 	struct em28xx      *dev   = fh->dev;
 
-	if (!dev->audio_mode.has_audio)
-		return -EINVAL;
-
 	switch (a->index) {
 	case EM28XX_AMUX_VIDEO:
 		strcpy(a->name, "Television");
@@ -1173,10 +1170,6 @@ static int vidioc_s_audio(struct file *file, void *priv, const struct v4l2_audio
 	struct em28xx_fh   *fh  = priv;
 	struct em28xx      *dev = fh->dev;
 
-
-	if (!dev->audio_mode.has_audio)
-		return -EINVAL;
-
 	if (a->index >= MAX_EM28XX_INPUT)
 		return -EINVAL;
 	if (0 == INPUT(a->index)->type)
@@ -1905,6 +1898,10 @@ int em28xx_register_analog_devices(struct em28xx *dev)
 		v4l2_disable_ioctl(dev->vdev, VIDIOC_G_FREQUENCY);
 		v4l2_disable_ioctl(dev->vdev, VIDIOC_S_FREQUENCY);
 	}
+	if (!dev->audio_mode.has_audio) {
+		v4l2_disable_ioctl(dev->vdev, VIDIOC_G_AUDIO);
+		v4l2_disable_ioctl(dev->vdev, VIDIOC_S_AUDIO);
+	}
 
 	/* register v4l2 video video_device */
 	ret = video_register_device(dev->vdev, VFL_TYPE_GRABBER,
@@ -1930,6 +1927,10 @@ int em28xx_register_analog_devices(struct em28xx *dev)
 			v4l2_disable_ioctl(dev->vbi_dev, VIDIOC_G_FREQUENCY);
 			v4l2_disable_ioctl(dev->vbi_dev, VIDIOC_S_FREQUENCY);
 		}
+		if (!dev->audio_mode.has_audio) {
+			v4l2_disable_ioctl(dev->vbi_dev, VIDIOC_G_AUDIO);
+			v4l2_disable_ioctl(dev->vbi_dev, VIDIOC_S_AUDIO);
+		}
 
 		/* register v4l2 vbi video_device */
 		ret = video_register_device(dev->vbi_dev, VFL_TYPE_VBI,