ASoC: dapm: Remove redundant clear_walk() for supply widgets

We already clear the walked state in dapm_widget_power_check(), no need
to do it again.

Signed-off-by: Ryo Tsutsui <Ryo.Tsutsui@wolfsonmicro.com>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>