usb: dwc3: st: prepare the driver for generic usb_get_dr_mode function

of_usb_get_dr_mode will be converted into more generic
usb_get_dr_mode function that will take struct device
instead of struct device_node as its parameter.

To make the conversion possible later, waiting for the
platform device for dwc3 to be populated before calling
of_usb_get_dr_mode.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
CC: Giuseppe Cavallaro <peppe.cavallaro@st.com>
CC: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/dwc3-st.c

@@ -195,6 +195,7 @@ static int st_dwc3_probe(struct platform_device *pdev)
 	struct resource *res;
 	struct device *dev = &pdev->dev;
 	struct device_node *node = dev->of_node, *child;
+	struct platform_device *child_pdev;
 	struct regmap *regmap;
 	int ret;
 
@@ -253,15 +254,22 @@ static int st_dwc3_probe(struct platform_device *pdev)
 		goto undo_softreset;
 	}
 
-	dwc3_data->dr_mode = of_usb_get_dr_mode(child);
-
 	/* Allocate and initialize the core */
 	ret = of_platform_populate(node, NULL, NULL, dev);
 	if (ret) {
 		dev_err(dev, "failed to add dwc3 core\n");
 		goto undo_softreset;
 	}
 
+	child_pdev = of_find_device_by_node(child);
+	if (!child_pdev) {
+		dev_err(dev, "failed to find dwc3 core device\n");
+		ret = -ENODEV;
+		goto undo_softreset;
+	}
+
+	dwc3_data->dr_mode = of_usb_get_dr_mode(child_pdev->dev.of_node);
+
 	/*
 	 * Configure the USB port as device or host according to the static
 	 * configuration passed from DT.