iio: health: max30100: correct FIFO check condition

Correct issue that the last entry in FIFO was being read twice due
to an incorrect decrement of entry count variable before condition
check.

Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/health/max30100.c b/drivers/iio/health/max30100.c
index 09db893..90ab8a2d 100644
--- a/drivers/iio/health/max30100.c
+++ b/drivers/iio/health/max30100.c
@@ -238,12 +238,13 @@
 
 	mutex_lock(&data->lock);
 
-	while (cnt-- || (cnt = max30100_fifo_count(data) > 0)) {
+	while (cnt || (cnt = max30100_fifo_count(data) > 0)) {
 		ret = max30100_read_measurement(data);
 		if (ret)
 			break;
 
 		iio_push_to_buffers(data->indio_dev, data->buffer);
+		cnt--;
 	}
 
 	mutex_unlock(&data->lock);