iio: accel: adxl367: do not update FIFO watermark on scan mode update

iio: accel: adxl367: do not update FIFO watermark on scan mode update

Currently, the driver updates the FIFO watermark inside both
update_scan_mode() and hwfifo_set_watermark(). Inside the IIO core,
hwfifo_set_watermark() is called immediately after update_scan_mode(),
making the first call to set_fifo_samples() redundant.

Remove the first call to set_fifo_samples(), and merge the
set_fifo_samples() function into the set_fifo_watermark()
function. Also, since fifo_set_size is always set inside of
update_scan_mode(), and it cannot be set to 0, remove the
zero check from set_fifo_samples().

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Link: https://lore.kernel.org/r/20220514182010.152784-1-cosmin.tanislav@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>