substream->runtime will be attached when substream was opened
at snd_pcm_attach_substream(). When it uses DPCM,
FE substream->runtime is attached, but BE substream->runtime is not.
Thus, we are copying FE substream->runtime to BE.

But, we are copyig FE substream->runtime to FE dpcm->runtime first (A),
and copy it to BE dpcm->runtime (B), and copy it to
BE substream->runtime (C).

	static int dpcm_fe_dai_open(...) {
		...
(A)		fe->dpcm[stream].runtime = fe_substream->runtime;
		...
	}

	static int dpcm_be_connect(...) {
		...
(B)		be->dpcm[stream].runtime = fe->dpcm[stream].runtime;
		...
	}

	int dpcm_be_dai_startup(...) {
		...
(C)		be_substream->runtime = be->dpcm[stream].runtime;
		...
	}

It is too roundabout and troublesome.
OTOH, it is directly copying fe_substream->runtime at dpcm_be_reparent()
without using be->dpcm[stream].runtime.

	static void dpcm_be_reparent(...)
	{
		...
		for_each_dpcm_fe(be, stream, dpcm) {
			...
=>			be_substream->runtime = fe_substream->runtime;
			break;
		}
	}

This patch removes indirect copying.
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87v8je64dh.wl-kuninori.morimoto.gx@renesas.comSigned-off-by: Mark Brown <broonie@kernel.org>