iio:ad5421: Mark transfer buffer as __be32

Fixes the following warnings from sparse:
	drivers/iio/dac/ad5421.c:134:25: warning: incorrect type in assignment (different base types)
	drivers/iio/dac/ad5421.c:134:25:    expected unsigned int [unsigned] [usertype] d32
	drivers/iio/dac/ad5421.c:134:25:    got restricted __be32 [usertype] <noident>
	drivers/iio/dac/ad5421.c:168:25: warning: incorrect type in assignment (different base types)
	drivers/iio/dac/ad5421.c:168:25:    expected unsigned int [unsigned] [usertype] d32
	drivers/iio/dac/ad5421.c:168:25:    got restricted __be32 [usertype] <noident>
	drivers/iio/dac/ad5421.c:172:23: warning: cast to restricted __be32
	drivers/iio/dac/ad5421.c:172:23: warning: cast to restricted __be32
	drivers/iio/dac/ad5421.c:172:23: warning: cast to restricted __be32
	drivers/iio/dac/ad5421.c:172:23: warning: cast to restricted __be32
	drivers/iio/dac/ad5421.c:172:23: warning: cast to restricted __be32
	drivers/iio/dac/ad5421.c:172:23: warning: cast to restricted __be32
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/dac/ad5421.c

@@ -75,7 +75,7 @@ struct ad5421_state {
 	 * transfer buffers to live in their own cache lines.
 	 */
 	union {
-		u32 d32;
+		__be32 d32;
 		u8 d8[4];
 	} data[2] ____cacheline_aligned;
 };