ASoC: Change how suspend and resume obtain the PCM runtime

Currently only the atmel driver make use of snd_soc_dai.runtime field.
If the dais are to be shared among two or more dai_links, the field
must be got rid of.
So, in atmel driver reach the substream via dai_link->pcm so as to
not depend of snd_soc_dai.runtime field.

Signed-off-by: Jassi Brar <jassi.brar@samsung.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>