[SCSI] aic94xx: Don't call pci_map_sg for already-mapped scatterlists

It turns out that libata has already dma_map_sg'd the scatterlist
entries that go with an ata_queued_cmd by the time it calls
sas_ata_qc_issue.  sas_ata_qc_issue passes this scatterlist to aic94xx.
Unfortunately, aic94xx assumes that any scatterlist passed to it needs
to be pci_map_sg'd... which blows away the mapping that libata created!
This causes (on a x260) Calgary IOMMU table leaks and duplicate frees
when aic94xx and libata try to {pci,dma}_unmap_sg the scatterlist.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>

Key this check off ATA_PROTOCOL_STP

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>