audio: fix parameter for tty_mode

Change-Id: Ic386415a1a62e133bbd5e9726240afd7e4dc301f
diff --git a/alsa_sound/AudioHardwareALSA.cpp b/alsa_sound/AudioHardwareALSA.cpp
index 4c63990..7343c63 100644
--- a/alsa_sound/AudioHardwareALSA.cpp
+++ b/alsa_sound/AudioHardwareALSA.cpp
@@ -288,11 +288,11 @@
     key = String8(TTY_MODE_KEY);
     if (param.get(key, value) == NO_ERROR) {
         mDevSettingsFlag &= TTY_CLEAR;
-        if (value == "full") {
+        if (value == "tty_full") {
             mDevSettingsFlag |= TTY_FULL;
-        } else if (value == "hco") {
+        } else if (value == "tty_hco") {
             mDevSettingsFlag |= TTY_HCO;
-        } else if (value == "vco") {
+        } else if (value == "tty_vco") {
             mDevSettingsFlag |= TTY_VCO;
         } else {
             mDevSettingsFlag |= TTY_OFF;