Make macro expansion-safe

Use parentheses to avoid unexpected results.

For example, make:

    2 * SERIALIZED_EVENT_MAX_SIZE

expand to:

    2 * (3 + TEXT_MAX_LENGTH)

instead of:

    2 * 3 + TEXT_MAX_LENGTH

app/src/control_event.h

@@ -10,7 +10,7 @@
 
 #define CONTROL_EVENT_QUEUE_SIZE 64
 #define TEXT_MAX_LENGTH 300
-#define SERIALIZED_EVENT_MAX_SIZE 3 + TEXT_MAX_LENGTH
+#define SERIALIZED_EVENT_MAX_SIZE (3 + TEXT_MAX_LENGTH)
 
 enum control_event_type {
     CONTROL_EVENT_TYPE_KEYCODE,