serial: max310x: fix NULL pointer dereference in I2C instantiation

When trying to instantiate a max14830 device from userspace:

    echo max14830 0x60 > /sys/bus/i2c/devices/i2c-2/new_device

we get the following error:

    Unable to handle kernel NULL pointer dereference at virtual address...
    ...
    Call trace:
        max310x_i2c_probe+0x48/0x170 [max310x]
        i2c_device_probe+0x150/0x2a0
    ...

Add check for validity of devtype to prevent the error, and abort probe
with a meaningful error message.

Fixes: 2e1f2d9a ("serial: max310x: implement I2C support")
Cc: stable@vger.kernel.org
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20240118152213.2644269-2-hugo@hugovil.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max310x.c

@@ -1602,13 +1602,16 @@ static unsigned short max310x_i2c_slave_addr(unsigned short addr,
 
 static int max310x_i2c_probe(struct i2c_client *client)
 {
-	const struct max310x_devtype *devtype =
-			device_get_match_data(&client->dev);
+	const struct max310x_devtype *devtype;
 	struct i2c_client *port_client;
 	struct regmap *regmaps[4];
 	unsigned int i;
 	u8 port_addr;
 
+	devtype = device_get_match_data(&client->dev);
+	if (!devtype)
+		return dev_err_probe(&client->dev, -ENODEV, "Failed to match device\n");
+
 	if (client->addr < devtype->slave_addr.min ||
 		client->addr > devtype->slave_addr.max)
 		return dev_err_probe(&client->dev, -EINVAL,