[PATCH] hwmon: (smsc47m1) fix outside array bounds warnings

[Masahiro Yamada]

Kbuild test robot reports outside array bounds warnings:

  CC [M]  drivers/hwmon/smsc47m1.o
drivers/hwmon/smsc47m1.c: In function 'fan_div_store':
drivers/hwmon/smsc47m1.c:370:49: warning: array subscript [0, 2] is outside array bounds of 'u8[3]' {aka 'unsigned char[3]'} [-Warray-bounds]
  tmp = 192 - (old_div * (192 - data->fan_preload[nr])
                                ~~~~~~~~~~~~~~~~~^~~~
drivers/hwmon/smsc47m1.c:372:19: warning: array subscript [0, 2] is outside array bounds of 'u8[3]' {aka 'unsigned char[3]'} [-Warray-bounds]
  data->fan_preload[nr] = clamp_val(tmp, 0, 191);
  ~~~~~~~~~~~~~~~~~^~~~
drivers/hwmon/smsc47m1.c:373:53: warning: array subscript [0, 2] is outside array bounds of 'const u8[3]' {aka 'const unsigned char[3]'} [-Warray-bounds]
  smsc47m1_write_value(data, SMSC47M1_REG_FAN_PRELOAD[nr],
                             ~~~~~~~~~~~~~~~~~~~~~~~~^~~~

The index field in the SENSOR_DEVICE_ATTR_R* defines is 0, 1, or 2.
However, the compiler never knows the fact that the default in the
switch statement is unreachable.

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
---

 drivers/hwmon/smsc47m1.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/hwmon/smsc47m1.c b/drivers/hwmon/smsc47m1.c
index 5f92eab24c62..e00102e05666 100644
--- a/drivers/hwmon/smsc47m1.c
+++ b/drivers/hwmon/smsc47m1.c
@@ -364,6 +364,10 @@ static ssize_t fan_div_store(struct device *dev,
 		tmp |= data->fan_div[2] << 4;
 		smsc47m1_write_value(data, SMSC47M2_REG_FANDIV3, tmp);
 		break;
+	default:
+		WARN_ON(1);
+		mutex_unlock(&data->update_lock);
+		return -EINVAL;
 	}
 
 	/* Preserve fan min */
-- 
2.17.1