async_pq_val: fix DMA memory leak

Add missing dmaengine_unmap_put(), so we don't OOM during RAID6 sync.

Fixes: 1786b943 ("async_pq_val: convert to dmaengine_unmap_data")
Signed-off-by: Justin Maggard <jmaggard@netgear.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

crypto/async_tx/async_pq.c

@@ -368,8 +368,6 @@ async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
 
 		dma_set_unmap(tx, unmap);
 		async_tx_submit(chan, tx, submit);
-
-		return tx;
 	} else {
 		struct page *p_src = P(blocks, disks);
 		struct page *q_src = Q(blocks, disks);
@@ -424,9 +422,11 @@ async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
 		submit->cb_param = cb_param_orig;
 		submit->flags = flags_orig;
 		async_tx_sync_epilog(submit);
-
-		return NULL;
+		tx = NULL;
 	}
+	dmaengine_unmap_put(unmap);
+
+	return tx;
 }
 EXPORT_SYMBOL_GPL(async_syndrome_val);