bnx2fc: fix incorrect DMA memory mapping in bnx2fc_unmap_sg_list()

This patch is based on a problem and solution from Maurizio Lombardi
where bnx2fc isn't consistent in which device struct we using for DMA
map and unmap operations.  Make them consistent by using dma_sg_unmap
in bnx2fc_unmap_sg_list like bnx2fc_map_sg.

Reviewed-by: Eddie Wai <eddie.wai@broadcom.com>
Signed-off-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>