Resolving 'SPI Device Not Ready' Error on AVR Microcontroller with Zephyr RTOS

SPI device not ready 

#include <zephyr.h>
#include <device.h>
#include <drivers/spi.h>
#include <logging/log.h>

LOG_MODULE_REGISTER(main);

#define MCP9808_SPI DT_NODELABEL(mcp9808)

static const struct spi_config spi_cfg = {
    .frequency = 1000000U,
    .operation = SPI_WORD_SET(8) | SPI_TRANSFER_MSB,
    .slave = 0,
    .cs = NULL,
};

void main(void) {
    const struct device *spi_dev = DEVICE_DT_GET(MCP9808_SPI);

    if (!device_is_ready(spi_dev)) {
        LOG_ERR("SPI device not ready");
        return;
    }

    uint8_t tx_buf[1] = {0x05}; // Register to read temperature
  uint8_t rx_buf[2];
    struct spi_buf tx = {.buf = tx_buf, .len = sizeof(tx_buf)};
    struct spi_buf rx = {.buf = rx_buf, .len = sizeof(rx_buf)};
    struct spi_buf_set tx_set = {.buffers = &tx, .count = 1};
    struct spi_buf_set rx_set = {.buffers = &rx, .count = 1};

    int ret = spi_transceive(spi_dev, &spi_cfg, &tx_set, &rx_set);
    if (ret) {
        LOG_ERR("SPI transceive failed: %d", ret);
        return;
    }


    int temp = ((rx_buf[0] << 8) | rx_buf[1]) & 0x0FFF;
    temp /= 16;

    LOG_INF("Temperature: %d C", temp);
}