Adding msm8660 back. Fixes lack of audio

Change-Id: I12a0bc5dd03a0fe0322db9dc14c3b1e4b015280e
When msm8660 was removed from the build list , audio became broken in some msm8660 devices, i.e. skyrocket. Adding a call pointing to hardware/qcom/audio-caf/legacy/msm8660 in hardware/qcom/audio-caf/Android.mk fixes this issue.