scsi: pm80xx: tag allocation for phy control request.

tag is taken from the tag pool instead of using the hardcoded tag
value(1).

Signed-off-by: Deepak Ukey <deepak.ukey@microsemi.com>
Signed-off-by: Viswas G <Viswas.G@microsemi.com>
Acked-by: Jack Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>