staging: r8188eu: Add support for Dlink DWA-121 802.11n Wireless N 150 Pico Adapter

This is a new device supported by this driver.

Signed-off-by: Kim Nylund <kim@pratsam.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>