parser: check (mut f Foo) syntax

vlib/sync/waitgroup.v

@@ -15,7 +15,7 @@ pub fn new_waitgroup() &WaitGroup {
 	return &WaitGroup{mu: sync.new_mutex() }
 }
 
-pub fn (wg mut WaitGroup) add(delta int) {
+pub fn (mut wg WaitGroup) add(delta int) {
 	wg.mu.lock()
 	wg.active += delta
 	wg.mu.unlock()
@@ -24,7 +24,7 @@ pub fn (wg mut WaitGroup) add(delta int) {
 	}
 }
 
-pub fn (wg mut WaitGroup) done() {
+pub fn (mut wg WaitGroup) done() {
 	wg.add(-1)
 }
 
@@ -39,4 +39,3 @@ pub fn (wg &WaitGroup) wait() {
 		}
 	}
 }
-