libstagefright:Fix random memcmp crash while accessing output format.

Random memcmp crash happens while checking for image-data in
output format of audio buffer.Audio output format gets updated with
pcm-format flag after codec formatchange in ExtendedNuUtils.
Simultaneous memory check happens for image-data in FBD of MediaCodec.
So crash happens.

Avoid checking for image-data and crop information for audio buffers.

Change-Id: I85ffcb149dc67a0f1bdb26116245627b1843d932