staging:iio:ad7746: Mark transfer buffer as __be32

Fixes the following warnings from sparse:
	drivers/staging/iio/cdc/ad7746.c:599:25: warning: cast to restricted __be32
	drivers/staging/iio/cdc/ad7746.c:599:25: warning: cast to restricted __be32
	drivers/staging/iio/cdc/ad7746.c:599:25: warning: cast to restricted __be32
	drivers/staging/iio/cdc/ad7746.c:599:25: warning: cast to restricted __be32
	drivers/staging/iio/cdc/ad7746.c:599:25: warning: cast to restricted __be32
	drivers/staging/iio/cdc/ad7746.c:599:25: warning: cast to restricted __be32

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/cdc/ad7746.c

@@ -567,7 +567,7 @@ static int ad7746_read_raw(struct iio_dev *indio_dev,
 	u8 regval, reg;
 
 	union {
-		u32 d32;
+		__be32 d32;
 		u8 d8[4];
 	} data;