master
Allows a driver to allocate and initialize a spi_device without registering it immediately. This allows a driver to directly fill the spi_device with device parameters before calling spi_add_device on it.
Caller is responsible to call spi_add_device on the returned spi_device structure to add it to the SPI master. If the caller needs to discard the spi_device without adding it, then it should call spi_dev_put on it.
Returns a pointer to the new device, or NULL.