VR: fix libvr_hwc-hal build

libhwcomposer-client was updated to use
android.hardware.graphics.mapper@2.0.

Bug: 37540361
Test: boots
Change-Id: Id9f94087a04890de95711c91ce9d5aa2f6c8e35d
diff --git a/services/vr/hardware_composer/Android.bp b/services/vr/hardware_composer/Android.bp
index 25bb30b..5cb201d 100644
--- a/services/vr/hardware_composer/Android.bp
+++ b/services/vr/hardware_composer/Android.bp
@@ -17,6 +17,7 @@
   shared_libs: [
     "android.frameworks.vr.composer@1.0",
     "android.hardware.graphics.composer@2.1",
+    "android.hardware.graphics.mapper@2.0",
     "libbase",
     "libcutils",
     "libfmq",