staging: mt7621: Add SPDX license identifier

Signed-off-by: Oliver Hübers <oliver.huebers@web.de>
Signed-off-by: Vanessa Borgmann <nessa.x@web.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-pci/pci-mt7621.c

+// SPDX-License-Identifier: GPL-2.0+
 /**************************************************************************
  *
  *  BRIEF MODULE DESCRIPTION