staging: rtl8188eu: Add device code for D-Link DWA-121 rev B1

This device was added to the stand-alone driver on github.
Add it to the staging driver as well.

Link: https://github.com/lwfinger/rtl8188eu/commit/a0619a07cd1e
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>