usb: cdns3: Fix runtime PM imbalance on error

When cdns3_gadget_start() fails, a pairing PM usage counter
decrement is needed to keep the counter balanced.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Link: https://lore.kernel.org/r/20210412054908.7975-1-dinghao.liu@zju.edu.cn


Signed-off-by: Peter Chen <peter.chen@kernel.org>