audioflinger: Fix effect creation handling

The code flow was incorrect for sure. The 'if' branch is chosen
if 'effect == 0', and 'effectRegistered' is set to 'true' before
the effect is even created.

Test: audioflinger doesn't crash if effect failed to get created
Change-Id: I00d5f28e8b96acd765867e212c5b8193e21f9b4a