libata: fix translation of concurrent positioning ranges

Fixing the page length in the SCSI translation for the concurrent
positioning ranges VPD page. It was writing starting in offset 3
rather than offset 2 where the MSB is supposed to start for
the VPD page length.

Cc: stable@vger.kernel.org
Fixes: fe22e1c2

 ("libata: support concurrent positioning ranges log")
Signed-off-by: Tyler Erickson <tyler.erickson@seagate.com>
Reviewed-by: Muhammad Ahmad <muhammad.ahmad@seagate.com>
Tested-by: Michael English <michael.english@seagate.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>