Staging: octeon-usb: Adding SPDX license identifier

Adding appropriate SPDX-License-Identifier (GPL-2) that were missing
from code, header and make files.
Signed-off-by: NGeorgios Tsotsos <tsotsos@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/octeon-usb/Makefile

+# SPDX-License-Identifier: GPL-2.0
 obj-${CONFIG_OCTEON_USB} := octeon-hcd.o

drivers/staging/octeon-usb/octeon-hcd.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * This file is subject to the terms and conditions of the GNU General Public
  * License.  See the file "COPYING" in the main directory of this archive

drivers/staging/octeon-usb/octeon-hcd.h

+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Octeon HCD hardware register definitions.
  *