Prevent object of AudioEffect be deleted until construction finished

The object of AudioEffect may be deleted when construction ongoing,
if the method of mIEffectClient invoked by the proxy in audioflinger.

If mIEffectClient cleared in the destructor of AudioEffect before IEffect
linkToDeath to mIEffectClient in the constructor of the AudioEffect,
the aforementioned case may lead to an abort, i.e.,
"Abort Message: 'linkToDeath():recipient must be non-NULL".

Test: monkey test
Change-Id: I5fe8227b8528fb9fb9c9a1e636bd4dc0cc22c2cf