iio: adc: mcp320x: Tidy up endian types in type cast.

Fixes the sparse warning:
drivers/iio/adc/mcp320x.c:167:41: warning: incorrect type in argument 1 (different base types)
drivers/iio/adc/mcp320x.c:167:41:    expected restricted __be32 const [usertype] *p
drivers/iio/adc/mcp320x.c:167:41:    got unsigned int [usertype] *<noident>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>

drivers/iio/adc/mcp320x.c

@@ -164,7 +164,7 @@ static int mcp320x_adc_conversion(struct mcp320x *adc, u8 channel,
 	case mcp3550_60:
 	case mcp3551:
 	case mcp3553: {
-		u32 raw = be32_to_cpup((u32 *)adc->rx_buf);
+		u32 raw = be32_to_cpup((__be32 *)adc->rx_buf);
 
 		if (!(adc->spi->mode & SPI_CPOL))
 			raw <<= 1; /* strip Data Ready bit in SPI mode 0,0 */