ASoC: dapm: Fix compilation warning

Fix following:
sound/soc/soc-dapm.c: In function ‘dapm_clock_event’:
sound/soc/soc-dapm.c:1021:1: warning: control reaches end of non-void function [-Wreturn-type]

Signed-off-by: Marek Belisko <marek.belisko@open-nandra.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>