staging: tegra-vde: Add SPDX GPL-2.0+ license identifier to fix checkpatch warning

Add the SPDX GPL-2.0+ license identifier to fix checkpatch.pl warning
"WARNING: Missing or malformed SPDX-License-Identifier tag in line 1"

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>