Use LOG_ALWAYS_FATAL instead of LOG_FATAL

LOG_FATAL is compiled out in most builds, so the
assertion checks were not being performed.

Change-Id: I774f0985ab9c5ccecd8989a0f1c940386b73fc35
diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index 90122e0..adb4aca 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -212,7 +212,7 @@
         case FastMixerState::MIX_WRITE:
             break;
         default:
-            LOG_FATAL("bad command %d", command);
+            LOG_ALWAYS_FATAL("bad command %d", command);
         }
 
         // there is a non-idle state available to us; did the state change?