iio:magnetometer:ak8975: fix uninitialized chipset

ak_def_array bounds are not properly checked in case of ACPI matching
failure. GCC warns with the following message at line 799:
‘chipset’ may be used uninitialized in this function.

Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/magnetometer/ak8975.c

@@ -774,8 +774,11 @@ static int ak8975_probe(struct i2c_client *client,
 	if (id) {
 		chipset = (enum asahi_compass_chipset)(id->driver_data);
 		name = id->name;
-	} else if (ACPI_HANDLE(&client->dev))
+	} else if (ACPI_HANDLE(&client->dev)) {
 		name = ak8975_match_acpi_device(&client->dev, &chipset);
+		if (!name)
+			return -ENODEV;
+	}
 	else
 		return -ENOSYS;