usb: dwc3: xilinx: fix uninitialized return value

usb: dwc3: xilinx: fix uninitialized return value

A previous patch to skip part of the initialization when a USB3 PHY was
not present could result in the return value being uninitialized in that
case, causing spurious probe failures. Initialize ret to 0 to avoid this.

Fixes: 9678f3361afc ("usb: dwc3: xilinx: Skip resets and USB3 register settings for USB2.0 mode")
Cc: <stable@vger.kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Link: https://lore.kernel.org/r/20220127221500.177021-1-robert.hancock@calian.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>