lpfc: Fix scsi prep dma buf error.

Didn't check for less-than-or-equal zero. Means we may later call
scsi_dma_unmap() even though we don't have valid mappings.

Signed-off-by: Dick Kennedy <dick.kennedy@avagotech.com>
Signed-off-by: James Smart <james.smart@avagotech.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>
diff --git a/drivers/scsi/lpfc/lpfc_scsi.c b/drivers/scsi/lpfc/lpfc_scsi.c
index 4a2a818..b3b195f 100644
--- a/drivers/scsi/lpfc/lpfc_scsi.c
+++ b/drivers/scsi/lpfc/lpfc_scsi.c
@@ -3257,7 +3257,7 @@
 		 */
 
 		nseg = scsi_dma_map(scsi_cmnd);
-		if (unlikely(!nseg))
+		if (unlikely(nseg <= 0))
 			return 1;
 		sgl += 1;
 		/* clear the last flag in the fcp_rsp map entry */