spi_master: add check for 'post_cb' when flag 'SPI_DEVICE_NO_RETURN_RESULT' is set

There are two ways to know which transaction descriptor is finished,
by either calling `spi_device_get_trans_result`, or getting it from `post_cb`.
When `SPI_DEVICE_NO_RETURN_RESULT` is set, driver will not push finished
transaction descriptors into the queue. So you can't get it from
`spi_device_get_trans_result`. The only way to know this is via `post_cb`.

update document for function `spi_bus_add_device`

components/driver/include/driver/spi_master.h

@@ -166,7 +166,8 @@ typedef struct spi_device_t *spi_device_handle_t;  ///< Handle for a device on a
  * @param dev_config SPI interface protocol config for the device
  * @param handle Pointer to variable to hold the device handle
  * @return
- *         - ESP_ERR_INVALID_ARG   if parameter is invalid
+ *         - ESP_ERR_INVALID_ARG   if parameter is invalid or configuration combination is not supported (e.g.
+ *                                 `dev_config->post_cb` isn't set while flag `SPI_DEVICE_NO_RETURN_RESULT` is enabled)
  *         - ESP_ERR_NOT_FOUND     if host doesn't have any free CS slots
  *         - ESP_ERR_NO_MEM        if out of memory
  *         - ESP_OK                on success