ASoC: Remove DAPM debugfs entries before freeing widgets

Remove the DAPM debugfs entries before freeing the context's widgets, otherwise a
use after free situation might occur.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>