Enable clang-tidy in oboeservice.

Warnings and errors generated by clang-tidy are eliminated by this CL.

Bug: 186572209
Test: make
Test: atest AAudioTests
Change-Id: I3296193bac18fee499f39314ac32a5750a385855
diff --git a/services/oboeservice/AAudioServiceEndpointPlay.cpp b/services/oboeservice/AAudioServiceEndpointPlay.cpp
index 2a5939f..637405d 100644
--- a/services/oboeservice/AAudioServiceEndpointPlay.cpp
+++ b/services/oboeservice/AAudioServiceEndpointPlay.cpp
@@ -158,5 +158,5 @@
 
     ALOGD("%s() exiting, enabled = %d, state = %d, result = %d <<<<<<<<<<<<< MIXER",
           __func__, mCallbackEnabled.load(), getStreamInternal()->getState(), result);
-    return NULL; // TODO review
+    return nullptr; // TODO review
 }