android: Return -EUSERS when failed to open a Camera that's in use

The correct return value for the HAL for hal_dev_open() when trying to
open a camera that's already opened is EUSERS. Make hal_dev_open()
return -EUSERS, and plumb the logic for this through
CameraHalManager::open().

This allows the following CTS tests to pass:
- android.hardware.camera2.cts.CameraManagerTest#testCameraManagerOpenAllCameras
- android.hardware.camera2.cts.MultiViewTest#testDualCameraPreview

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/android/camera_hal_manager.h

@@ -10,6 +10,7 @@
 #include <map>
 #include <mutex>
 #include <stddef.h>
+#include <tuple>
 #include <vector>
 
 #include <hardware/camera_common.h>
@@ -28,7 +29,8 @@ public:
 
 	int init();
 
-	CameraDevice *open(unsigned int id, const hw_module_t *module);
+	std::tuple<CameraDevice *, int>
+	open(unsigned int id, const hw_module_t *module);
 
 	unsigned int numCameras() const;
 	int getCameraInfo(unsigned int id, struct camera_info *info);