libnbaio: Add libaudioutils headers export

Header files of libnbaio include files from audio_utils
yet the module did not export include path for those. This was
requiring modules depending on libnbaio[_mono] to add those
include paths into their build files.

Test: make
Change-Id: I8982e04db0f3646ce7945fb55529727766f2dfa1
diff --git a/media/libnbaio/Android.bp b/media/libnbaio/Android.bp
index a4df38d..6345742 100644
--- a/media/libnbaio/Android.bp
+++ b/media/libnbaio/Android.bp
@@ -1,4 +1,3 @@
-
 cc_defaults {
     name: "libnbaio_mono_defaults",
     srcs: [
@@ -21,6 +20,9 @@
         "liblog",
         "libutils",
     ],
+    export_shared_lib_headers: [
+        "libaudioutils",
+    ],
 
     export_include_dirs: ["include_mono"],
 }
@@ -66,7 +68,5 @@
         "-Wall",
     ],
 
-    include_dirs: ["system/media/audio_utils/include"],
-
     export_include_dirs: ["include"],
 }