Use correct LOCAL_MODULE_TARGET_ARCH for x86_64

valgrind uses amd64 arch name where android build system
uses x86_64. The build file has a substitute for that but
that substitute was mistakenly used for LOCAL_MODULE_TARGET_ARCH
which lead to omitted x86_64 binaries for target builds.

Bug: http://b/30964325
Test: Build aosp_x86_64 and make sure amd64 binaries are present in
Test: out/target/product/generic_x86_64/system/lib64/valgrind/
Change-Id: I6ede1948aaadeea6f01329cd007bcd62e5a4d19f
diff --git a/Android.clean.mk b/Android.clean.mk
index 31ae7f4..ed0a053 100644
--- a/Android.clean.mk
+++ b/Android.clean.mk
@@ -12,7 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
+vg_local_android_arch :=
+vg_local_arch :=
 vg_local_module :=
 vg_local_target :=
 vg_local_module_class :=