[SCSI] 3w-9xxx: fix iommu_iova leak

Following reports on the list, it looks like the 3e-9xxx driver will leak dma
mappings every time we get a transient queueing error back from the card.
This is because it maps the sg list in the routine that sends the command, but
doesn't unmap again in the transient failure path (even though the command is
sent back to the block layer).  Fix by unmapping before returning the status.

Reported-by: Chris Boot <bootc@bootc.net>
Tested-by: Chris Boot <bootc@bootc.net>
Acked-by: Adam Radford <aradford@gmail.com>
Cc: stable@kernel.org
Signed-off-by: James Bottomley <JBottomley@Parallels.com>