pata_hpt3x2n: fix clock turnaround

The clock turnaround code still doesn't work for several reasons:

- 'USE_DPLL' flag in 'ap->host->private_data' is never initialized
  or updated, so the driver can only set the chip to the DPLL clock
  mode, not the PCI mode;

- the driver doesn't serialize access to the channels depending on
  the current clock mode like the vendor drivers, so the clock
  turnaround is only executed "optionally", not always as it should be;

- the wrong ports are written to when hpt3x2n_set_clock() is called
  for the secondary channel;

- hpt3x2n_set_clock() can inadvertently enable the disabled channels
  when resetting the channel state machines.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>