staging: vme: vme_user: add SPDX identifier.

It's good to have SPDX identifiers in all files to make it easier to
audit the kernel tree for correct licenses.

Fix up the remaining staging vme driver to have a proper SPDX
identifier, based on the license text in the file itself.  The SPDX
identifier is a legally binding shorthand, which can be used instead of
the full boiler plate text.

This work is based on a script and data from Thomas Gleixner, Philippe
Ombredanne, and Kate Stewart.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Martyn Welch <martyn@welchs.me.uk>
Cc: Manohar Vanga <manohar.vanga@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vme/devices/vme_user.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * VMEbus User access driver
  *