sstorage: fix vendor linker error

Fix the following error showing up when trying to build the secure
storage example on AOSP.

  external/optee_examples/secure_storage/Android.mk: error:
  optee_example_secure_storage (native:platform) should not link to
  libteec (native:vendor)

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/secure_storage/Android.mk b/secure_storage/Android.mk
index 84e540f..6deae5b 100644
--- a/secure_storage/Android.mk
+++ b/secure_storage/Android.mk
@@ -13,6 +13,7 @@
 
 LOCAL_SHARED_LIBRARIES := libteec
 LOCAL_MODULE := optee_example_secure_storage
+LOCAL_VENDOR_MODULE := true
 LOCAL_MODULE_TAGS := optional
 include $(BUILD_EXECUTABLE)