I had a similar problem, i just Corrected the location of the JNI in the code(D2xx class) to the proper one i.e from the default location to "/data/data/com.ftdi.d2xx/lib/libftd2xx-jni.so".
By the way the driver you are using needs root access. A new driver has been released by FTDI which they say doesn't require root access. Just check that out from their website FTDI Android D2xx Driver