Stop abusing ide_lock lock (switch to a private locking).

Fixes same issue as fixed by Alan Cox in atiixp host driver with
commit 6c5f8cc3.

Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>