iio: adc: ina2xx: remove unused debug field from chip global data

commit 1961bce7 "iio: ina2xx: Remove trace_printk debug
statements" removed the code that used the chip->prev_ns field.
This patch cleans it up further by removing the unused field
and assignments.
Signed-off-by: NAlison Schofield <amsfield22@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/iio/adc/ina2xx-adc.c

@@ -114,7 +114,6 @@ struct ina2xx_chip_info {
 	struct mutex state_lock;
 	unsigned int shunt_resistor;
 	int avg;
-	s64 prev_ns; /* track buffer capture time, check for underruns */
 	int int_time_vbus; /* Bus voltage integration time uS */
 	int int_time_vshunt; /* Shunt voltage integration time uS */
 	bool allow_async_readout;
@@ -509,8 +508,6 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev)
 	iio_push_to_buffers_with_timestamp(indio_dev,
 					   (unsigned int *)data, time_a);
 
-	chip->prev_ns = time_a;
-
 	return (unsigned long)(time_b - time_a) / 1000;
 };
 
@@ -554,8 +551,6 @@ static int ina2xx_buffer_enable(struct iio_dev *indio_dev)
 	dev_dbg(&indio_dev->dev, "Async readout mode: %d\n",
 		chip->allow_async_readout);
 
-	chip->prev_ns = iio_get_time_ns(indio_dev);
-
 	chip->task = kthread_run(ina2xx_capture_thread, (void *)indio_dev,
 				 "%s:%d-%uus", indio_dev->name, indio_dev->id,
 				 sampling_us);