ehci: fix port count.

#define FRAME_TIMER_NS   (1000000000 / FRAME_TIMER_FREQ)

#define NB_MAXINTRATE    8        // Max rate at which controller issues ints

#define NB_PORTS         4        // Number of downstream ports

#define NB_PORTS         6        // Number of downstream ports

#define BUFF_SIZE        5*4096   // Max bytes to transfer per transaction

#define MAX_ITERATIONS   20       // Max number of QH before we break the loop

#define MAX_QH           100      // Max allowable queue heads in a chain