Input: msg2638 - only read linux,keycodes array if necessary

The linux,keycodes property is optional.
Fix the driver not probing when it's not specified.

Fixes: c18ef503 ("Input: msg2638 - add support for msg2138 key events")
Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
Link: https://lore.kernel.org/r/20221130210202.2069213-1-vincent.knecht@mailoo.orgSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/msg2638.c

@@ -412,6 +412,7 @@ static int msg2638_ts_probe(struct i2c_client *client)
 		msg2638->num_keycodes = ARRAY_SIZE(msg2638->keycodes);
 	}
 
+	if (msg2638->num_keycodes > 0) {
 		error = device_property_read_u32_array(dev, "linux,keycodes",
 						       msg2638->keycodes,
 						       msg2638->num_keycodes);
@@ -420,6 +421,7 @@ static int msg2638_ts_probe(struct i2c_client *client)
 				error);
 			return error;
 		}
+	}
 
 	error = devm_request_threaded_irq(dev, client->irq,
 					  NULL, chip_data->irq_handler,