Since the goal is to have the MAX3421E working, which uses multiple 8
bit transfers, we should support multiple 8 bit transfers instead of
trying to use 16 bit transfers.
When using spi_byte(), the device is automatically selected. After you
have made as many transfers as you want, you must deselect the device
with spi_deselect().
the SPI module reads and writes at the same time. If you don't want to
write a value, then write all zeros or whatever the device you are
communicating with wants.
