ASoC: ti: edma-pcm: Fix for legacy dma_slave_map based channel lookup

Most of the daVinci devices does not boot with DT. In this case the DMA
channel is looked up with dma_slave_map and for that the chan_names[]
must be configured.

Both McASP and ASP/McBSP uses "tx" and "rx" as channel names, so we can
just do this when the dev->of_node is not valid.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20190830103841.25128-4-peter.ujfalusi@ti.com


Signed-off-by: Mark Brown <broonie@kernel.org>