hwmon: (w83792d) Fix NULL pointer dereference by removing unnecessary structure field

If driver read val value sufficient for
(val & 0x08) && (!(val & 0x80)) && ((val & 0x7) == ((val >> 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: stable@vger.kernel.org
Signed-off-by: Nadezda Lutovinova <lutovinova@ispras.ru>
Link: https://lore.kernel.org/r/20210921155153.28098-2-lutovinova@ispras.ru
[groeck: Dropped unnecessary continuation lines, fixed multipline alignment]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: Nadezda Lutovinova

drivers/hwmon/w83792d.c

@@ -264,9 +264,6 @@ struct w83792d_data {
 	char valid;		/* !=0 if following fields are valid */
 	unsigned long last_updated;	/* In jiffies */
 
-	/* array of 2 pointers to subclients */
-	struct i2c_client *lm75[2];
-
 	u8 in[9];		/* Register value */
 	u8 in_max[9];		/* Register value */
 	u8 in_min[9];		/* Register value */
@@ -927,7 +924,6 @@ w83792d_detect_subclients(struct i2c_client *new_client)
 	int address = new_client->addr;
 	u8 val;
 	struct i2c_adapter *adapter = new_client->adapter;
-	struct w83792d_data *data = i2c_get_clientdata(new_client);
 
 	id = i2c_adapter_id(adapter);
 	if (force_subclients[0] == id && force_subclients[1] == address) {
@@ -946,21 +942,19 @@ w83792d_detect_subclients(struct i2c_client *new_client)
 	}
 
 	val = w83792d_read_value(new_client, W83792D_REG_I2C_SUBADDR);
-	if (!(val & 0x08))
-		data->lm75[0] = devm_i2c_new_dummy_device(&new_client->dev, adapter,
-							  0x48 + (val & 0x7));
-	if (!(val & 0x80)) {
-		if (!IS_ERR(data->lm75[0]) &&
-			((val & 0x7) == ((val >> 4) & 0x7))) {
-			dev_err(&new_client->dev,
-				"duplicate addresses 0x%x, use force_subclient\n",
-				data->lm75[0]->addr);
-			return -ENODEV;
-		}
-		data->lm75[1] = devm_i2c_new_dummy_device(&new_client->dev, adapter,
-							  0x48 + ((val >> 4) & 0x7));
+
+	if (!(val & 0x88) && (val & 0x7) == ((val >> 4) & 0x7)) {
+		dev_err(&new_client->dev,
+			"duplicate addresses 0x%x, use force_subclient\n", 0x48 + (val & 0x7));
+		return -ENODEV;
 	}
 
+	if (!(val & 0x08))
+		devm_i2c_new_dummy_device(&new_client->dev, adapter, 0x48 + (val & 0x7));
+
+	if (!(val & 0x80))
+		devm_i2c_new_dummy_device(&new_client->dev, adapter, 0x48 + ((val >> 4) & 0x7));
+
 	return 0;
 }