mfd: 88pm860x: Fix possible NULL pointer dereference on i2c_new_dummy error

During probe the driver allocates dummy I2C device for companion chip
with i2c_new_dummy() but it does not check the return value of this call.

In case of error (i2c_new_device(): memory allocation failure or I2C
address cannot be used) this function returns NULL which is later used
by regmap_init_i2c().

If i2c_new_dummy() fails for companion device, fail also the probe for
main MFD driver.

Cc: stable@vger.kernel.org
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/88pm860x-core.c

@@ -1179,6 +1179,11 @@ static int pm860x_probe(struct i2c_client *client,
 		chip->companion_addr = pdata->companion_addr;
 		chip->companion = i2c_new_dummy(chip->client->adapter,
 						chip->companion_addr);
+		if (!chip->companion) {
+			dev_err(&client->dev,
+				"Failed to allocate I2C companion device\n");
+			return -ENODEV;
+		}
 		chip->regmap_companion = regmap_init_i2c(chip->companion,
 							&pm860x_regmap_config);
 		if (IS_ERR(chip->regmap_companion)) {