iio: chemical: sps30: Explicity truncate constant by masking

When breaking up a constant to write to two 8 bit registers
it isn't obvious to sparse that it was intentional.

CHECK   drivers/iio/chemical/sps30.c
drivers/iio/chemical/sps30.c:120:30: warning: cast truncates bits from constant value (8004 becomes 4)

So in the interests of minimising noisy warnings, let us add
a mask.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Tomasz Duszynski <tduszyns@gmail.com>

drivers/iio/chemical/sps30.c

@@ -117,7 +117,7 @@ static int sps30_do_cmd(struct sps30_state *state, u16 cmd, u8 *data, int size)
 		break;
 	case SPS30_READ_AUTO_CLEANING_PERIOD:
 		buf[0] = SPS30_AUTO_CLEANING_PERIOD >> 8;
-		buf[1] = (u8)SPS30_AUTO_CLEANING_PERIOD;
+		buf[1] = (u8)(SPS30_AUTO_CLEANING_PERIOD & 0xff);
 		/* fall through */
 	case SPS30_READ_DATA_READY_FLAG:
 	case SPS30_READ_DATA: