drivers: ssd16xx: fix driver initialization

ssd16xx driver is not well designed and does not pass configuration
via device->config but via struct ssd16xx_data, this was not taken
into account in the commit 4d6d50e2bc
("display: ssd16xx: convert to spi_dt_spec").

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>

drivers/display/ssd16xx.c

@@ -636,8 +636,8 @@ static int ssd16xx_controller_init(const struct device *dev)
 
 static int ssd16xx_init(const struct device *dev)
 {
-	const struct ssd16xx_config *config = dev->config;
 	struct ssd16xx_data *driver = dev->data;
+	const struct ssd16xx_config *config = driver->config;
 
 	LOG_DBG("");