[Non-BE] Add fix NONBE_1246_INF_COHERENCE_IN_HIGH_LEVEL_DTX to port MR1919

This is a small fix that just adds a parenthesis to change the order of calculation and avoid an overflow/Inf in the coherence calculation.

@vaillancour, I put you as reviewer it is non-BE and since you reviewed ivas-codec-pc/ivas-codec!1919 (merged). It is a trivial change.

The issue was that the multiplication with coh_weight was done before the division, and these numbers could go to Inf. By adding parentheses, the division is done first and the problem was solved.