frontend/va: Create decoder once the max_references is updated

Issue: When a video is decoded where the max_references is updated the
decoder keeps using same old value. This results into green patches and
decoding is not proper.

Root Cause: The max_references is updated only once when the instance is
created for the first time.

Fix: Added a check along with the context->decoder to check if the
context->templat.max_references has changed. If yes, then we go ahead
and create the decoder again.

Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Krunal Patel <krunalkumarmukeshkumar.patel@amd.corp-partner.google.com>
Part-of: <!15750>