usb/max3421: fix return error code in max3421_probe()

usb/max3421: fix return error code in max3421_probe()

retval may be reassigned to 0 after max3421_of_vbus_en_pin(),
if allocate memory failed after this, max3421_probe() cann't
return ENOMEM, fix this by moving assign retval afther max3421_probe().

Fixes: 721fdc83b31b ("usb: max3421: Add devicetree support")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20201117061500.3454223-1-yangyingliang@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>