NTB: Fix static check warning in perf_clear_test

As pthr->dma_chan can't be NULL in this context, so there is
no need to check pthr->dma_chan.

Fixes: 99a0605612 ("NTB: ntb_perf: Fix address err in perf_copy_chunk")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jiasen Lin <linjiasen@hygon.cn>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/test/ntb_perf.c

@@ -1010,7 +1010,7 @@ static void perf_clear_test(struct perf_thread *pthr)
 				   pthr->perf->test_peer->dma_dst_addr,
 				   pthr->perf->test_peer->outbuf_size,
 				   DMA_FROM_DEVICE, 0);
-	if (pthr->dma_chan)
+
 	dma_release_channel(pthr->dma_chan);
 
 no_dma_notify: