usb: dwc3: st: Fix node's child name

Update node's child name from "dwc3" to "usb", this fixes
the following issue:

[3.773852] usb-st-dwc3 8f94000.dwc3: failed to find dwc3 core node

Fixes: 3120910 ("ARM: dts: stih407-family: Harmonize DWC USB3 DT nodes name")
Reported-by: Jerome Audu <jerome.audu@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Link: https://lore.kernel.org/r/20220926124359.304770-1-patrice.chotard@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Patrice Chotard

drivers/usb/dwc3/dwc3-st.c

@@ -251,7 +251,7 @@ static int st_dwc3_probe(struct platform_device *pdev)
 	/* Manage SoftReset */
 	reset_control_deassert(dwc3_data->rstc_rst);
 
-	child = of_get_child_by_name(node, "dwc3");
+	child = of_get_child_by_name(node, "usb");
 	if (!child) {
 		dev_err(&pdev->dev, "failed to find dwc3 core node\n");
 		ret = -ENODEV;