Minor optimize for dispatch_queue_async_safe

@@ -89,7 +89,7 @@ FOUNDATION_EXPORT NSString *const SDWebImageErrorDomain;
 
 #ifndef dispatch_queue_async_safe
 #define dispatch_queue_async_safe(queue, block)\
-    if (strcmp(dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL), dispatch_queue_get_label(queue)) == 0) {\
+    if (dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL) == dispatch_queue_get_label(queue)) {\
         block();\
     } else {\
         dispatch_async(queue, block);\