ASoC: Fix dapm_seq_compare() for multi-component

Ensure that we keep all widget powerups in DAPM sequence by making
the CODEC the last thing we compare on rather than the first thing.
Also fix the fact that we're currently comparing the widget pointers
rather than the CODEC pointers when we do the substraction so we
won't get stable results.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>