Making codebase C90-compliant

dnn/dump_data.c

dnn/lpcnet.c

dnn/lpcnet_dec.c

dnn/lpcnet_enc.c

dnn/lpcnet_plc.c

dnn/nnet.c

dnn/pitch.c

dnn/pitch.h

dnn/vec.h

dnn/vec_avx.h