ntb: ntb_perf missing dmaengine_unmap_put

In the normal I/O execution path, ntb_perf is missing a call to
dmaengine_unmap_put() after submission. That causes us to leak
unmap objects.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Fixes: 8a7b6a77 ("ntb: ntb perf tool")
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/test/ntb_perf.c

@@ -265,6 +265,8 @@ static ssize_t perf_copy(struct pthr_ctx *pctx, char __iomem *dst,
 	if (dma_submit_error(cookie))
 		goto err_set_unmap;
 
+	dmaengine_unmap_put(unmap);
+
 	atomic_inc(&pctx->dma_sync);
 	dma_async_issue_pending(chan);