Fixed the step_size_bytes in the ADPCM Accelerator loop

Fixed the step_size_bytes in the ADPCM Accelerator loop taking into account the varying number of bytes that ADPCM steps by.
Thanks @magumagu, I saw how bad I was with arithmetic last night.

It's also looking like the calculation for step_size_bytes in the ADPCM case is not correct at all (Address & 15).  Do you have any ideas on how I can calculate step_size_bytes for ADPCM?