usb: dwc3: no need to initialize ret variable

usb: dwc3: no need to initialize ret variable

First usage of ret variable will re-write initial value. Thus, there is no need
to initialize it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>