ASoC: lpass-platform: fix uninitialized variable

In commit 022d00ee ("ASoC: lpass-platform: Fix broken pcm data
usage") the stream specific information initialization was broken, with
the dma channel information not being initialized if there was no
alloc_dma_channel() helper function.

Before that, the DMA channel number was implicitly initialized to zero
because the backing store was allocated with devm_kzalloc().  When the
init code was rewritten, that implicit initialization was lost, and gcc
rightfully complains about an uninitialized variable being used.

Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>