usb: dwc2: Switch to use device_property_count_u32()

Use use device_property_count_u32() directly, that makes code neater.

Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>