audioflinger: modify fast mixer overrun management

Do not force sleep when an overrun occurs. This was for non
blocking audio HAL and is unused.
Keep statistics on overruns.

Bug 6605215.

Change-Id: I295455d4562201aa3814c88bdd6e52c9226712af
diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index d8bed40..3bb7b44 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -483,7 +483,10 @@
                                 (int) sec, nsec / 1000000L);
                         dumpState->mOverruns++;
                     }
-                    sleepNs = periodNs - overrunNs;
+                    // Code for non blocking audio HAL. Sleep time must be tuned to allow
+                    // catching up after an underrun
+                    //     sleepNs = periodNs - overrunNs;
+                    sleepNs = -1;
                 } else {
                     sleepNs = -1;
                     ignoreNextOverrun = false;