Issue #2083 - Fix scraping for mixer devices.

The list of mixer devices was limited to 1 due to 'head -1' in
the command pipeline.  This means you could only every set
and persist the first mixer device of a card.

Remove the 'head -1' call so all mixer devices are scraped.

Author: octalthorpe

src/boot/FPPINIT.cpp

@@ -1091,13 +1091,13 @@ static void setupAudio() {
         break;
     }
     PutFileContents("/root/.asoundrc", asoundrc);
-    std::string mixers = execAndReturn("/usr/bin/amixer -c " + std::to_string(card) + " scontrols | head -1 | cut -f2 -d\"'\"");
+    std::string mixers = execAndReturn("/usr/bin/amixer -c " + std::to_string(card) + " scontrols | cut -f2 -d\"'\"");
     if (mixers.empty()) {
         // for some sound cards, the mixer devices won't show up
         // until something is played.  Play one second of silence
         exec("/usr/bin/aplay -d 1 /opt/fpp/media/silence_5sec.wav >> /dev/null 2>&1  &");
         std::this_thread::sleep_for(std::chrono::milliseconds(200));
-        mixers = execAndReturn("/usr/bin/amixer -c " + std::to_string(card) + " scontrols | head -1 | cut -f2 -d\"'\"");
+        mixers = execAndReturn("/usr/bin/amixer -c " + std::to_string(card) + " scontrols | cut -f2 -d\"'\"");
     }
     TrimWhiteSpace(mixers);
     std::string mixer;