spi_chunk_init
spi_chunk_init(&sc->sc_spi_chunk, 2, (const void *)&sc->sc_pinstate, NULL);
spi_chunk_init(&chunk, cnt, NULL, data);
spi_chunk_init(&chunk, cnt, data, NULL);
spi_chunk_init(&chunk1, scnt, snd, NULL);
spi_chunk_init(&chunk2, rcnt, NULL, rcv);
spi_chunk_init(&ce->chunk, iov[c].iov_len, iov[c].iov_base, NULL);
spi_chunk_init(&chunk1, addrlen + 1, buf, NULL);
spi_chunk_init(&chunk2, cnt, wdata, rdata);
void spi_chunk_init(struct spi_chunk *, int, const uint8_t *, uint8_t *);