Rework enc/dec mismatch detection

Rework enc/dec mismatch detection

The previous enc/dec mismatch detection assumes the previously
reconstructed frame would always stay at frame buffer pool index
at 0. It could hence cause certain delay in enc/dec mismatch
detection when the immediate reconstruction frame is not yet
propagated to index 0 in the buffer map pool.

This change always keeps the latest decoded show frame buffer
index and directly gets the reconstructed frame from encoder and
decoder buffer pools to check for mismatch.

Change-Id: If53092cbc42ab78d55af5b83f12a489fc362f3ae