EffectsFactory: fix subeffects loading

Due to a error in code, effects loaded via libproxy were
not populated correctly when the new XML effects format
was used.

Bug: 37492580
Test: no "AudioFlinger could not create effect" error messages
      when enabling effects in Play Music

Change-Id: I15b4f20060397662c98835cdf8af9fa198ea994f
1 file changed