iio: dac: ad5758: 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/dac/ad5758.ko | grep alias
alias:          spi:ad5758

After this patch:
modinfo drivers/iio/dac/ad5758.ko | grep alias
alias:          spi:ad5758
alias:          of:N*T*Cadi,ad5758C*
alias:          of:N*T*Cadi,ad5758
Reported-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Daniel Gomez <dagmcr@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/ad5758.c

@@ -11,6 +11,8 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/property.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
 #include <linux/spi/spi.h>
 #include <linux/gpio/consumer.h>
 
@@ -885,9 +887,16 @@ static const struct spi_device_id ad5758_id[] = {
 };
 MODULE_DEVICE_TABLE(spi, ad5758_id);
 
+static const struct of_device_id ad5758_of_match[] = {
+        { .compatible = "adi,ad5758" },
+        { },
+};
+MODULE_DEVICE_TABLE(of, ad5758_of_match);
+
 static struct spi_driver ad5758_driver = {
 	.driver = {
 		.name = KBUILD_MODNAME,
+		.of_match_table = ad5758_of_match,
 	},
 	.probe = ad5758_probe,
 	.id_table = ad5758_id,