PCI: endpoint: functions/pci-epf-test: Fix dma_chan direction

PCI: endpoint: functions/pci-epf-test: Fix dma_chan direction

In pci_epf_test_init_dma_chan() epf_test->dma_chan_rx is assigned from
dma_request_channel() with DMA_DEV_TO_MEM as filter.dma_mask.

However, in pci_epf_test_data_transfer() if the dir is DMA_DEV_TO_MEM,
epf->dma_chan_rx should be used but instead we are using
epf_test->dma_chan_tx.

Fix it.

Link: https://lore.kernel.org/r/20230412063447.2841177-1-yoshihiro.shimoda.uh@renesas.com
Fixes: 8353813c88ef ("PCI: endpoint: Enable DMA tests for endpoints with DMA capabilities")
Tested-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>