iio: adc: max1027: fix error code in max1027_wait_eoc()

Return -ETIMEDOUT on timeout instead of success.

Fixes: 1f7b4048 ("iio: adc: max1027: Use the EOC IRQ when populated for single reads")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>