libata-zpodd: must use ata_tf_init()

There are  some SATA controllers which have both devices 0 and 1 but this module
just zeroes out taskfile and sets then ATA_TFLAG_DEVICE (not sure that's needed)
which could  lead to a wrong device being selected just before issuing command.
Thus we should  call ata_tf_init()  which sets  up the device register value
properly, like  all other users of ata_exec_internal() do...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org