i2c: slave: print warning if slave flag not set

Address collisions will be rare, but we should let the user know that
slaves have their own address space nonetheless.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/i2c-core.c

@@ -3017,6 +3017,10 @@ int i2c_slave_register(struct i2c_client *client, i2c_slave_cb_t slave_cb)
 		return -EINVAL;
 	}
 
+	if (!(client->flags & I2C_CLIENT_SLAVE))
+		dev_warn(&client->dev, "%s: client slave flag not set. You might see address collisions\n",
+			 __func__);
+
 	if (!(client->flags & I2C_CLIENT_TEN)) {
 		/* Enforce stricter address checking */
 		ret = i2c_check_7bit_addr_validity_strict(client->addr);