Avoid clash with "register" keyword

This fixes a Doxygen warning where a (seemingly) non-existent parameter was
documented.

types.h

@@ -375,10 +375,10 @@ typedef int  (*JackSampleRateCallback)(jack_nframes_t nframes, void *arg);
  *
  * @param port the ID of the port
  * @param arg pointer to a client supplied data
- * @param register non-zero if the port is being registered,
- *                     zero if the port is being unregistered
+ * @param registered non-zero if the port is being registered,
+ *                       zero if the port is being unregistered
  */
-typedef void (*JackPortRegistrationCallback)(jack_port_id_t port, int /* register */, void *arg);
+typedef void (*JackPortRegistrationCallback)(jack_port_id_t port, int registered, void *arg);
 
 /**
  * Prototype for the client supplied function that is called
@@ -396,11 +396,11 @@ typedef void (*JackPortRenameCallback)(jack_port_id_t port, const char* old_name
  * whenever a client is registered or unregistered.
  *
  * @param name a null-terminated string containing the client name
- * @param register non-zero if the client is being registered,
- *                     zero if the client is being unregistered
+ * @param registered non-zero if the client is being registered,
+ *                       zero if the client is being unregistered
  * @param arg pointer to a client supplied data
  */
-typedef void (*JackClientRegistrationCallback)(const char* name, int /* register */, void *arg);
+typedef void (*JackClientRegistrationCallback)(const char* name, int registered, void *arg);
 
 /**
  * Prototype for the client supplied function that is called