SoftAMR: Signal the right frame format

The correct enum for the format used is OMX_AUDIO_AMRFrameFormatFSF,
which is the same as is used in amrnb/enc/SoftAMRNBEncoder.cpp,
amrwbenc/SoftAMRWBEncoder.cpp and in OMXCodec and ACodec.

The OMX_AUDIO_AMRFrameFormatConformance enum refers to an odd file
format only used for conformance tests, not used in the wild.

Change-Id: Idc395fc1d4969e33453522d6ec6526876438c526