libcamera: controls: Revert incorrect SPDX removal

In commit 6a09deaf7d ("controls: Add FrameWallClock control") the
existing SPDX was accidentally removed, likely from a rebase operation
at some point.

Unfortunately as this patch had already collected Reviewed-by tags, the
surruptious removal wasn't noticed until after it was merged.

Re-insert the existing SPDX and copyright banner as the header to the
control definitions file.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/control_ids_core.yaml

@@ -1,4 +1,6 @@
-
+# SPDX-License-Identifier: LGPL-2.1-or-later
+#
+# Copyright (C) 2019, Google Inc.
 #
 %YAML 1.1
 ---