dsp: asm: validate ADSP data size before access

Check the size of ADSP payload before accessing it.
Validate buffer index obtained from ADSP token before using it.

CRs-Fixed: 2372302
Change-Id: I3f5e1b6f515935a10a8c59c324452be0a71f9473
Signed-off-by: Vignesh Kulothungan <vigneshk@codeaurora.org>