fix compilation error with 'PathSpec redefined'

src/service.h

@@ -25,6 +25,7 @@
 typedef struct Service Service;
 
 #include "unit.h"
+#include "path.h"
 #include "ratelimit.h"
 
 typedef enum ServiceState {
@@ -86,8 +87,6 @@ typedef enum NotifyAccess {
         _NOTIFY_ACCESS_INVALID = -1
 } NotifyAccess;
 
-typedef struct PathSpec PathSpec;
-
 struct Service {
         Meta meta;