ata: sata_sx4: drop already completed TODO

The TODO claims that the pdc_20621_ops should set the .inherits
function pointer to &ata_base_port_ops after it has been converted
to use the new EH.

However, the driver was converted to use the new EH a long time ago,
in commit 67651ee5 ("[libata] sata_sx4: convert to new exception
handling methods"), which also did set .inherits function pointer to
&ata_sff_port_ops (and ata_sff_port_ops itself has .inherits set to
&ata_base_port_ops).

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>