audio policy: configurable engine: fix dead lock issue

This patch fixes a dead lock issue within configurable engine
of the audio policy. A clear was calling itself in loop instead
of calling clear on its base class.

Change-Id: I9f7c5f6425fbba36e029664ac130cbeafeca4ddf
Signed-off-by: François Gaffie <francois.gaffie@intel.com>