Add log tag for bufferhub service

Fix: 119820885
Test: patch ag/5557446, run BufferHubBuffer_test,
then verify that there are log messages with
bufferhubservice tag and logs with bufferhub tag.

Change-Id: I76fa244ee2ca8b26850ca455caa988baba5ab5d5
diff --git a/services/bufferhub/Android.bp b/services/bufferhub/Android.bp
index 28a7501..b747dbc 100644
--- a/services/bufferhub/Android.bp
+++ b/services/bufferhub/Android.bp
@@ -17,6 +17,7 @@
 cc_library_shared {
     name: "libbufferhubservice",
     cflags: [
+        "-DLOG_TAG=\"libbufferhubservice\"",
         "-Wall",
         "-Werror",
         "-Wextra",
@@ -71,6 +72,7 @@
         "libutils",
     ],
     cflags: [
+        "-DLOG_TAG=\"bufferhub\"",
         "-Wall",
         "-Werror",
         "-Wextra",