iio: temperature: maxim_thermocouple: declare missing of table

Add missing <of_device_id> table for SPI driver relying on SPI
device match since compatible is in a DT binding or in a DTS.

Before this patch:
modinfo drivers/iio/temperature/maxim_thermocouple.ko | grep alias
alias:          spi:max31855
alias:          spi:max6675

After this patch:
modinfo drivers/iio/temperature/maxim_thermocouple.ko | grep alias
alias:          spi:max31855
alias:          spi:max6675
alias:          of:N*T*Cmaxim,max31855C*
alias:          of:N*T*Cmaxim,max31855
alias:          of:N*T*Cmaxim,max6675C*
alias:          of:N*T*Cmaxim,max6675
Reported-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Daniel Gomez <dagmcr@gmail.com>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/temperature/maxim_thermocouple.c

@@ -10,6 +10,8 @@
 #include <linux/init.h>
 #include <linux/mutex.h>
 #include <linux/err.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
 #include <linux/spi/spi.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/trigger.h>
@@ -262,9 +264,17 @@ static const struct spi_device_id maxim_thermocouple_id[] = {
 };
 MODULE_DEVICE_TABLE(spi, maxim_thermocouple_id);
 
+static const struct of_device_id maxim_thermocouple_of_match[] = {
+        { .compatible = "maxim,max6675" },
+        { .compatible = "maxim,max31855" },
+        { },
+};
+MODULE_DEVICE_TABLE(of, maxim_thermocouple_of_match);
+
 static struct spi_driver maxim_thermocouple_driver = {
 	.driver = {
 		.name	= MAXIM_THERMOCOUPLE_DRV_NAME,
+		.of_match_table = maxim_thermocouple_of_match,
 	},
 	.probe		= maxim_thermocouple_probe,
 	.remove		= maxim_thermocouple_remove,