[Complexity] Optimize ivas_param_mc_dec_render_fx()

Basic info

This is a sub-task of issue #1009 (closed).

Bug description

The function ivas_param_mc_dec_render_fx() determines twice whether mixing_matrix_fx and mixing_matrix_res_fx are all zero - this is relatively complex and can be optimized in a bit-exact manner.

Ways to reproduce

See commandline in issue #1009 (closed).