ASoC: dwc: Drop DMA channel names assignment

The dw_configure_dai_by_dt() function and further dev->{play,capture}
_dma_data.dt data structures seem to be used in this driver only in case
of a system using devicetree, thus chan_name assignments have no effect
since they will be ignored in dmaengine_pcm_request_chan_of() call and
will be substituted with values taken form dmaengine_pcm_dma_channel_names[]
table ("tx", "rx").

Also there is no any "TX", "RX" dma-names entries in arch/arm/boot/dts,
only lower case "tx", "rx" seem to be used.

Lastly, this driver doesn't set SND_DMAENGINE_PCM_FLAG_CUSTOM_CHANNEL_NAME
flag when registering a dmaengine PCM to indicate the chan_name should be
used.

My intention is to eventually remove the struct snd_dmaengine_dai_dma_data
chan_name field as there is also a chan_names[] field in struct
snd_dmaengine_pcm_config which can be used for same purpose.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>