[ALSA] emu10k1 - Fix STAC9758 front channel

For some time now, some users of STAC9758 (emu10k1) would have no sound on
their front channels. This can be fixed (at least for me) by unmuting  head
phone volume and setting it to 0dB before removing the 'Front Playback'
control. For details, cf.
https://bugtrack.alsa-project.org/alsa-bug/view.php?id=2308
Find the appropriate patch attached.
Credits to: Raymond

Signed-off-by: Rolf Stefan Wilke <stefan.wilke@uni-ulm.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/pci/emu10k1/emumixer.c

@@ -1582,6 +1582,7 @@ int __devinit snd_emu10k1_mixer(struct snd_emu10k1 *emu,
 			if (emu->ac97->id == AC97_ID_STAC9758) {
 				emu->rear_ac97 = 1;
 				snd_emu10k1_ptr_write(emu, AC97SLOT, 0, AC97SLOT_CNTR|AC97SLOT_LFE|AC97SLOT_REAR_LEFT|AC97SLOT_REAR_RIGHT);
+				snd_ac97_write_cache(emu->ac97, AC97_HEADPHONE, 0x0202);
 			}
 			/* remove unused AC97 controls */
 			snd_ac97_write_cache(emu->ac97, AC97_SURROUND_MASTER, 0x0202);