staging: rtl8712: Add device ID for Sitecom WLA2100

This adds the USB ID for the Sitecom WLA2100. The Windows 10 inf file
was checked to verify that the addition is correct.

Reported-by: Frans van de Wiel <fvdw@fvdw.eu>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Frans van de Wiel <fvdw@fvdw.eu>
Cc: Stable <stable@vger.kernel.org> [All stable versions]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>