iio: adc: ad7280a: handle spi_setup() errors in probe()

The probe() function ignored the return value of spi_setup(), leaving SPI
configuration failures undetected. If spi_setup() fails, the driver should
stop initialization and propagate the error to the caller.

Add proper error handling: check the return value of spi_setup() and return
it on failure.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 2051f25 ("iio: adc: New driver for AD7280A Lithium Ion Battery Monitoring System")
Signed-off-by: Pavel Zhigulin <Pavel.Zhigulin@kaspersky.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: Pavel Zhigulin

drivers/iio/adc/ad7280a.c

@@ -1024,7 +1024,9 @@ static int ad7280_probe(struct spi_device *spi)
 
 	st->spi->max_speed_hz = AD7280A_MAX_SPI_CLK_HZ;
 	st->spi->mode = SPI_MODE_1;
-	spi_setup(st->spi);
+	ret = spi_setup(st->spi);
+	if (ret < 0)
+		return ret;
 
 	st->ctrl_lb = FIELD_PREP(AD7280A_CTRL_LB_ACQ_TIME_MSK, st->acquisition_time) |
 		FIELD_PREP(AD7280A_CTRL_LB_THERMISTOR_MSK, st->thermistor_term_en);