mfd: omap-usb-host: Make of_device_id array const

Array of struct of_device_id may be be const as expected by
of_platform_populate() call.
Signed-off-by: NKrzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

drivers/mfd/omap-usb-host.c

@@ -557,7 +557,7 @@ static int usbhs_omap_get_dt_pdata(struct device *dev,
 	return 0;
 }
 
-static struct of_device_id usbhs_child_match_table[] = {
+static const struct of_device_id usbhs_child_match_table[] = {
 	{ .compatible = "ti,omap-ehci", },
 	{ .compatible = "ti,omap-ohci", },
 	{ }