iio: temperature: ltc2983: make bulk write buffer DMA-safe

regmap_bulk_write() does not guarantee implicit DMA-safety,
even though the current implementation duplicates the given
buffer. Do not rely on it.

Fixes: f110f318 ("iio: temperature: Add support for LTC2983")
Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Link: https://lore.kernel.org/r/20221103130041.2153295-2-demonsingur@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/temperature/ltc2983.c

@@ -209,6 +209,7 @@ struct ltc2983_data {
 	 * Holds the converted temperature
 	 */
 	__be32 temp __aligned(IIO_DMA_MINALIGN);
+	__be32 chan_val;
 };
 
 struct ltc2983_sensor {
@@ -313,19 +314,18 @@ static int __ltc2983_fault_handler(const struct ltc2983_data *st,
 	return 0;
 }
 
-static int __ltc2983_chan_assign_common(const struct ltc2983_data *st,
+static int __ltc2983_chan_assign_common(struct ltc2983_data *st,
 					const struct ltc2983_sensor *sensor,
 					u32 chan_val)
 {
 	u32 reg = LTC2983_CHAN_START_ADDR(sensor->chan);
-	__be32 __chan_val;
 
 	chan_val |= LTC2983_CHAN_TYPE(sensor->type);
 	dev_dbg(&st->spi->dev, "Assign reg:0x%04X, val:0x%08X\n", reg,
 		chan_val);
-	__chan_val = cpu_to_be32(chan_val);
-	return regmap_bulk_write(st->regmap, reg, &__chan_val,
-				 sizeof(__chan_val));
+	st->chan_val = cpu_to_be32(chan_val);
+	return regmap_bulk_write(st->regmap, reg, &st->chan_val,
+				 sizeof(st->chan_val));
 }
 
 static int __ltc2983_chan_custom_sensor_assign(struct ltc2983_data *st,