iio: ak8975: fix maybe-uninitialized warning

If i2c_device_id *id is NULL and acpi_match_device returns NULL too,
then chipset may be unitialized when accessing &ak_def_array[chipset] in
ak8975_probe. Therefore initialize chipset to AK_MAX_TYPE, which will
return an error when not changed.

This patch fixes the following maybe-uninitialized warning:

drivers/iio/magnetometer/ak8975.c: In function ‘ak8975_probe’:
drivers/iio/magnetometer/ak8975.c:788:14: warning: ‘chipset’ may be used
uninitialized in this function [-Wmaybe-uninitialized]
  data->def = &ak_def_array[chipset];
Signed-off-by: Richard Leitner <dev@g0hl1n.net>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/magnetometer/ak8975.c

@@ -732,7 +732,7 @@ static int ak8975_probe(struct i2c_client *client,
 	int eoc_gpio;
 	int err;
 	const char *name = NULL;
-	enum asahi_compass_chipset chipset;
+	enum asahi_compass_chipset chipset = AK_MAX_TYPE;
 
 	/* Grab and set up the supplied GPIO. */
 	if (client->dev.platform_data)