V4L/DVB (11979): em28xx: don't create audio device if not supported

In cases where the device does not actually provide a USB audio class *or*
vendor audio, do not load the driver that provides vendor audio support (such
as the KWorld 2800d).  Otherwise, the /dev/audio1 device file gets created and
users get confused.

Also, reworks the logic a bit so that we don't try to inspect the register
content if the register read failed entirely.
Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

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

@@ -500,17 +500,20 @@ int em28xx_audio_setup(struct em28xx *dev)
 
 	/* See how this device is configured */
 	cfg = em28xx_read_reg(dev, EM28XX_R00_CHIPCFG);
-	if (cfg < 0)
-		cfg = EM28XX_CHIPCFG_AC97; /* Be conservative */
-	else
 	em28xx_info("Config register raw data: 0x%02x\n", cfg);
-
-	if ((cfg & EM28XX_CHIPCFG_AUDIOMASK) ==
+	if (cfg < 0) {
+		/* Register read error?  */
+		cfg = EM28XX_CHIPCFG_AC97; /* Be conservative */
+	} else if ((cfg & EM28XX_CHIPCFG_AUDIOMASK) == 0x00) {
+		/* The device doesn't have vendor audio at all */
+		dev->has_alsa_audio = 0;
+		dev->audio_mode.has_audio = 0;
+		return 0;
+	} else if ((cfg & EM28XX_CHIPCFG_AUDIOMASK) ==
 		   EM28XX_CHIPCFG_I2S_3_SAMPRATES) {
 		em28xx_info("I2S Audio (3 sample rates)\n");
 		dev->audio_mode.i2s_3rates = 1;
-	}
-	if ((cfg & EM28XX_CHIPCFG_AUDIOMASK) ==
+	} else if ((cfg & EM28XX_CHIPCFG_AUDIOMASK) ==
 		   EM28XX_CHIPCFG_I2S_5_SAMPRATES) {
 		em28xx_info("I2S Audio (5 sample rates)\n");
 		dev->audio_mode.i2s_5rates = 1;