Use correct pid when running under test harness

This is a partial fix which addresses one of the root causes of this bug,
but only when running under test harness.  It has no effect otherwise.

Bug: 8598539
Change-Id: I87444daef1d76b17544f331e651ba1c87893c381
diff --git a/services/audioflinger/ServiceUtilities.h b/services/audioflinger/ServiceUtilities.h
index f77ec5b..80cecba 100644
--- a/services/audioflinger/ServiceUtilities.h
+++ b/services/audioflinger/ServiceUtilities.h
@@ -18,7 +18,7 @@
 
 namespace android {
 
-extern const pid_t getpid_cached;
+extern pid_t getpid_cached;
 
 bool recordingAllowed();
 bool settingsAllowed();