Set error code while device ID query failed.

Fixes: 88bc3054 ("IIO: ADC: New driver for AD7792/AD7793 3 Channel SPI ADC")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>