PCI: endpoint: Remove surplus return statement from pci_epf_test_clean_dma_chan()

Remove a surplus return statement from the void function that has been
added in the commit commit 8353813 ("PCI: endpoint: Enable DMA
tests for endpoints with DMA capabilities").

Especially, as an empty return statements at the end of a void functions
serve little purpose.

This fixes the following checkpatch.pl script warning:

  WARNING: void function return statements are not generally useful
  #296: FILE: drivers/pci/endpoint/functions/pci-epf-test.c:296:
  +     return;
  +}

Link: https://lore.kernel.org/r/tencent_F250BEE2A65745A524E2EFE70CF615CA8F06@qq.com
Signed-off-by: Wang Jiang <jiangwang@kylinos.cn>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Author: Wang Jiang

drivers/pci/endpoint/functions/pci-epf-test.c

@@ -291,8 +291,6 @@ static void pci_epf_test_clean_dma_chan(struct pci_epf_test *epf_test)
 
 	dma_release_channel(epf_test->dma_chan_rx);
 	epf_test->dma_chan_rx = NULL;
-
-	return;
 }
 
 static void pci_epf_test_print_rate(struct pci_epf_test *epf_test,