Fix incorrect order of arguments in prototype (#887)

The prototype of pg_setup_standby_mode() in the pgctl.h header file
listed the argument in the wrong order compared to the implementation.
The type of the arguments were equal so it still compiled fine.

src/bin/pg_autoctl/pgctl.h

@@ -61,8 +61,8 @@ int pg_ctl_status(const char *pg_ctl, const char *pgdata, bool log_output);
 bool pg_ctl_promote(const char *pg_ctl, const char *pgdata);
 
 bool pg_setup_standby_mode(uint32_t pg_control_version,
-						   const char *pg_ctl,
 						   const char *pgdata,
+						   const char *pg_ctl,
 						   ReplicationSource *replicationSource);
 
 bool pg_cleanup_standby_mode(uint32_t pg_control_version,