Fix bionic-unit-tests

Fix rpath value for libraries after build system update

Bug: http://b/31221587
Test: run bionic-unit-tests --gtest_filter=dl*:Dl*:*atexit*
Change-Id: Iaed834bef830fd0b252b5de82e27634bafc92d8b
diff --git a/tests/libs/Android.bp b/tests/libs/Android.bp
index 8283633..e1a4239 100644
--- a/tests/libs/Android.bp
+++ b/tests/libs/Android.bp
@@ -18,7 +18,7 @@
     name: "bionic_testlib_defaults",
     host_supported: true,
     ldflags: [
-        "-Wl,--rpath,\\$${ORIGIN}",
+        "-Wl,--rpath,${ORIGIN}",
         "-Wl,--enable-new-dtags",
     ],
     relative_install_path: "bionic-loader-test-libs",