Resolving issues reported with decod_gen_2sbfr_ivas_fx()

[x] Updated Wrong scaling when going from float
to fixed point for Aq, causing Overflow in syn_filt_s_lc_fx()
[x] Fix for issue when computing the excitation in
decod_gen_2sbfr_ivas_fx()
[x] Addressed uninitialized variables used in
decod_gen_2sbfr_ivas_fx() + call to enhancer_fx
has wrong parameters.