iio: adc: mcp320x: Set struct spi_driver .of_match_table

The driver has an OF id table but the .of_match_table is not set so
the SPI core can't do an OF style match and the table was unused.
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Michael Welling <mwelling@ieee.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/mcp320x.c

@@ -404,6 +404,7 @@ MODULE_DEVICE_TABLE(spi, mcp320x_id);
 static struct spi_driver mcp320x_driver = {
 	.driver = {
 		.name = "mcp320x",
+		.of_match_table = of_match_ptr(mcp320x_dt_ids),
 		.owner = THIS_MODULE,
 	},
 	.probe = mcp320x_probe,