old_inp_16k_fx potentially wrong scale in stereo_mdct_core_enc_fx()

Basic info

Bug description

The buffer old_inp_16k_fx was originally scaled to Q0 and back to Q_new-1, but after merge of !2553 (merged) the scale is inconsistent.

Ways to reproduce

Box folder: ...\Box_EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-xxxx