camera2 ndk: Fix vndk error return value for ACameraManager::OpenCamera().

Bug: 147402004

Test: make hidl connectDevice return Status::DISCONNECTED.
      Run AImageReaderVendorTest. See that
      ACameraManager::openCamera() returns ACAMERA_ERROR_DISCONNECTED.

Change-Id: I3bcf0be54d1b9e88baa0b22350d74c0370ad23a6
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>