iio: stmpe-adc: use of_device_id for OF matching

The of_device_id was added to allow module autoloading, but it should be
also used to allow driver matching via Devicetree.

This also fixes W=1 warning:
  drivers/iio/adc/stmpe-adc.c:357:34: error: ‘stmpe_adc_ids’ defined but not used [-Werror=unused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220501103447.111392-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stmpe-adc.c

@@ -345,21 +345,22 @@ static int __maybe_unused stmpe_adc_resume(struct device *dev)
 
 static SIMPLE_DEV_PM_OPS(stmpe_adc_pm_ops, NULL, stmpe_adc_resume);
 
+static const struct of_device_id stmpe_adc_ids[] = {
+	{ .compatible = "st,stmpe-adc", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, stmpe_adc_ids);
+
 static struct platform_driver stmpe_adc_driver = {
 	.probe		= stmpe_adc_probe,
 	.driver		= {
 		.name	= "stmpe-adc",
 		.pm	= &stmpe_adc_pm_ops,
+		.of_match_table = stmpe_adc_ids,
 	},
 };
 module_platform_driver(stmpe_adc_driver);
 
-static const struct of_device_id stmpe_adc_ids[] = {
-	{ .compatible = "st,stmpe-adc", },
-	{ },
-};
-MODULE_DEVICE_TABLE(of, stmpe_adc_ids);
-
 MODULE_AUTHOR("Stefan Agner <stefan.agner@toradex.com>");
 MODULE_DESCRIPTION("STMPEXXX ADC driver");
 MODULE_LICENSE("GPL v2");