ASoC: SOF: Intel: hda: fix null deref on system suspend entry

In the Linux kernel, the following vulnerability has been resolved:

ASoC: SOF: Intel: hda: fix null deref on system suspend entry

When system enters suspend with an active stream, SOF core

calls hw_params_upon_resume(). On Intel platforms with HDA DMA used

to manage the link DMA, this leads to call chain of

hda_dsp_set_hw_params_upon_resume()

-> hda_dsp_dais_suspend()

-> hda_dai_suspend()

-> hda_ipc4_post_trigger()

A bug is hit in hda_dai_suspend() as hda_link_dma_cleanup() is run first,

which clears hext_stream->link_substream, and then hda_ipc4_post_trigger()

is called with a NULL snd_pcm_substream pointer.