ASoC: ti: Fix SDMA users not providing channel names

McBSP used to work correctly as long as compat DMA probing, removed by
commit 642aafea ("ASoC: ti: remove compat dma probing"), was
available.  New method of DMA probing apparently requires users to
provide channel names when registering with SDMA, while McBSP passes
NULLs.  Fix it.

The same probably applies to McASP (not tested), hence the patch fixes
both.

Fixes: 642aafea ("ASoC: ti: remove compat dma probing")
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>