libata: transport: Remove circular dependency at free time

Without this patch, failed probe would not free resources like irq.

ata port tdev object currently hold a reference to the ata port
object.  Therefore the ata port object release function will not get
called until the ata_tport_release is called. But that would never
happen, releasing the last reference of ata port dev is done by
scsi_host_release, which is called by ata_host_release when the ata
port object is released.

The ata device objects actually do not need to explicitly hold a
reference to their real counterpart, given the transport objects are
the children of these objects and device_add() is call for each child.
We know the parent will not be deleted until we call the child's
device_del().

Reported-by: Matthew Whitehead <tedheadster@gmail.com>
Tested-by: Matthew Whitehead <tedheadster@gmail.com>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Tejun Heo <tj@kernel.org>