Fix tap reset

Previous tap reset was made by doing 'statewalk(0x1F, 6, 0);' thus sending five 1 to TAP.
But we need to send five 1 plus one 0 to terminate TAP RESET so 'statewalk(0x3E, 7, 0);' is correct.
Moreover, it is preferable to check if 'ftdi_write_data' return exactly 3. In this case, if it write only one or two byte(s), it would pass security check but would'nt be OK.