staging:rtl8192u: Add SPDX-License-Identifier tag - Style

Add the missing SPDX-License-Identifier tag to clear the checkpatch
issue. This is a coding style change which should not impact runtime
code execution.
Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/r8190_rtl8256.h

+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  *	 This is part of the rtl8180-sa2400 driver
  *	 released under the GPL (See file COPYING for details).