scsi: libsas: make use of ata_port_is_frozen() helper

Clean up the code by making use of the newly introduced
ata_port_is_frozen() helper function.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>