libadf: adf_test: fix clang + kati build

kati needs us to add "tests" as a subdir of the libadf Android.bp.
clang also requires an explicit definition of AdfTest::dev_id where
g++ does not.

Test: mmm system/core/adf/libadf
Test: /data/nativetest64/adf-unit-tests/adf-unit-tests (on Nexus 9)
Change-Id: I1fc371af1b5b115f088edd963a87e6647a52882b
Signed-off-by: Greg Hackmann <ghackmann@google.com>
diff --git a/adf/libadf/Android.bp b/adf/libadf/Android.bp
index 2b5461e..1a81a49 100644
--- a/adf/libadf/Android.bp
+++ b/adf/libadf/Android.bp
@@ -19,3 +19,5 @@
     local_include_dirs: ["include"],
     export_include_dirs: ["include"],
 }
+
+subdirs = ["tests"]
diff --git a/adf/libadf/tests/adf_test.cpp b/adf/libadf/tests/adf_test.cpp
index 01b2785..eaa9342 100644
--- a/adf/libadf/tests/adf_test.cpp
+++ b/adf/libadf/tests/adf_test.cpp
@@ -149,11 +149,13 @@
     int eng;
 
 private:
-    const static adf_id_t dev_id = 0;
+    const static adf_id_t dev_id;
     const static __u32 fmt8888[];
     const static size_t n_fmt8888;
 };
 
+const adf_id_t AdfTest::dev_id = 0;
+
 const __u32 AdfTest::fmt8888[] = {
    DRM_FORMAT_XRGB8888,
    DRM_FORMAT_XBGR8888,