ALSA: opl3sa2: add ZV port control

Add ZV port control switch.

This patch is done after solution
given in the ALSA bug #2872 report.
The patch resolves the issue.
Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/opl3sa2.c

@@ -481,6 +481,7 @@ OPL3SA2_DOUBLE_TLV("Master Playback Volume", 0, 0x07, 0x08, 0, 0, 15, 1,
 OPL3SA2_SINGLE("Mic Playback Switch", 0, 0x09, 7, 1, 1),
 OPL3SA2_SINGLE_TLV("Mic Playback Volume", 0, 0x09, 0, 31, 1,
 		   db_scale_5bit_12db_max),
+OPL3SA2_SINGLE("ZV Port Switch", 0, 0x02, 0, 1, 0),
 };
 
 static struct snd_kcontrol_new snd_opl3sa2_tone_controls[] = {