[Complexity] Optimize ivas_param_mc_dec_render_fx()
# Basic info
This is a sub-task of issue #1009.
# 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.
issue