When a DAPM context has a prefix the autodisable widgets get prefixed
twice, once for the control and once for the widget. To avoid this use
the un-prefixed control name to construct the autodisable widget name.

This change is purely cosmetic.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NMark Brown <broonie@kernel.org>