staging: fix go7007-usb license

Add MODULE_LICENSE() as per the license in the comment at the top of the
file for this source module to fix build warning:

  WARNING: modpost: missing MODULE_LICENSE() in drivers/staging/media/go7007/go7007-usb.o
  see include/linux/module.h for more information

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Ross Cohen <rcohen@snurgle.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>