ASoC: soc-topology.c: dai_link->platform again

On SOF, many topology is assuming dai_link->platform exists, and is
allowed to be overwritten on each link_load().
This patch restore the removed dai_link->platform for SOF, and add
the comment.

Fixes: e7098ba9 ("ASoC: soc-topology.c: remove unnecessary dai_link->platform")
Reported-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://lore.kernel.org/r/87jzz7jczp.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://lore.kernel.org/r/87v8ikcsr5.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>