Fixes a bunch of 16-bit issues that the C5X compiler warns about

celt/rate.h

silk/CNG.c

silk/Inlines.h

silk/LPC_inv_pred_gain.c

silk/LP_variable_cutoff.c

silk/NLSF_VQ_weights_laroia.c

silk/NLSF_decode.c

silk/NLSF_del_dec_quant.c

silk/NSQ.c

silk/NSQ_del_dec.c

silk/PLC.c

silk/VAD.c

silk/control_codec.c

silk/dec_API.c

silk/decode_core.c

silk/fixed/apply_sine_window_FIX.c

silk/fixed/burg_modified_FIX.c

silk/fixed/find_LTP_FIX.c

silk/fixed/find_pred_coefs_FIX.c

silk/fixed/noise_shape_analysis_FIX.c