hwmon: (adc128d818) Do proper sign extension

data->temp[index] has type s16. Because of C's promotion rules,
(data->temp[index] << 7) >> 7 is exactly the same as
data->temp[index]. The intention was to use bit 8 as a sign bit, so do
that using the existing API.

Signed-off-by: Rasmus Villemoes <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/adc128d818.c

···
 #include <linux/err.h>
 #include <linux/regulator/consumer.h>
 #include <linux/mutex.h>
+#include <linux/bitops.h>
 
 /* Addresses to scan
  * The chip also supports addresses 0x35..0x37. Don't scan those addresses
···
 	if (IS_ERR(data))
 		return PTR_ERR(data);
 
-	temp = (data->temp[index] << 7) >> 7;	/* sign extend */
+	temp = sign_extend32(data->temp[index], 8);
 	return sprintf(buf, "%d\n", temp * 500);/* 0.5 degrees C resolution */
 }