hwmon: (w83793) Fix NULL pointer dereference by removing unnecessary structure field

If driver read tmp value sufficient for
(tmp & 0x08) && (!(tmp & 0x80)) && ((tmp & 0x7) == ((tmp >> 4) & 0x7))
from device then Null pointer dereference occurs.
(It is possible if tmp = 0b0xyz1xyz, where same literals mean same numbers)
Also lm75[] does not serve a purpose anymore after switching to
devm_i2c_new_dummy_device() in w83791d_detect_subclients().

The patch fixes possible NULL pointer dereference by removing lm75[].

Found by Linux Driver Verification project (linuxtesting.org).

Cc: [e-mail]
Signed-off-by: Nadezda Lutovinova <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[groeck: Dropped unnecessary continuation lines, fixed multi-line alignments]
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/w83793.c

···
 }
 
 struct w83793_data {
-	struct i2c_client *lm75[2];
 	struct device *hwmon_dev;
 	struct mutex update_lock;
 	char valid;			/* !=0 if following fields are valid */
···
 	int address = client->addr;
 	u8 tmp;
 	struct i2c_adapter *adapter = client->adapter;
-	struct w83793_data *data = i2c_get_clientdata(client);
 
 	id = i2c_adapter_id(adapter);
 	if (force_subclients[0] == id && force_subclients[1] == address) {
···
 	}
 
 	tmp = w83793_read_value(client, W83793_REG_I2C_SUBADDR);
-	if (!(tmp & 0x08))
-		data->lm75[0] = devm_i2c_new_dummy_device(&client->dev, adapter,
-							  0x48 + (tmp & 0x7));
-	if (!(tmp & 0x80)) {
-		if (!IS_ERR(data->lm75[0])
-		    && ((tmp & 0x7) == ((tmp >> 4) & 0x7))) {
-			dev_err(&client->dev,
-				"duplicate addresses 0x%x, "
-				"use force_subclients\n", data->lm75[0]->addr);
-			return -ENODEV;
-		}
-		data->lm75[1] = devm_i2c_new_dummy_device(&client->dev, adapter,
-							  0x48 + ((tmp >> 4) & 0x7));
+
+	if (!(tmp & 0x88) && (tmp & 0x7) == ((tmp >> 4) & 0x7)) {
+		dev_err(&client->dev,
+			"duplicate addresses 0x%x, use force_subclient\n", 0x48 + (tmp & 0x7));
+		return -ENODEV;
 	}
+
+	if (!(tmp & 0x08))
+		devm_i2c_new_dummy_device(&client->dev, adapter, 0x48 + (tmp & 0x7));
+
+	if (!(tmp & 0x80))
+		devm_i2c_new_dummy_device(&client->dev, adapter, 0x48 + ((tmp >> 4) & 0x7));
 
 	return 0;
 }