iio: adc: ad4630: Mask AD4630_REG_AVG to prevent UB

The value read from the AD4630_REG_AVG register is fine if it matches
the documentation. Be a bit more prudent though and mask the value to
the intended value. Still more as shifts bigger than the variable's
width result in undefined behaviour.

Also simplify

	var *= 1 << shift

to

	var <<= shift

.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>

Author: ukleinek

drivers/iio/adc/ad4630.c

@@ -77,6 +77,8 @@
 #define AD4630_CLK_MODE_MSK		GENMASK(5, 4)
 #define AD4630_DATA_RATE_MODE_MSK	BIT(3)
 #define AD4630_OUT_DATA_MODE_MSK	GENMASK(2, 0)
+/* AVG */
+#define AD4630_AVG_AVG_VAL		GENMASK(4, 0)
 /* OFFSET */
 #define AD4630_REG_CHAN_OFFSET(ch)	(AD4630_REG_OFFSET_X0_2 + 3 * (ch))
 /* HARDWARE_GAIN */
@@ -395,7 +397,7 @@ static int __ad4630_set_sampling_freq(const struct ad4630_state *st, unsigned in
 		if (ret)
 			return ret;
 
-		fetch_state.period *= 1 << avg;
+		fetch_state.period <<= FIELD_GET(AD4630_AVG_AVG_VAL, avg);
 	}
 
 	/*