lv_refr: remove unneccesary waiting for flush

lv_core/lv_refr.c

@@ -220,8 +220,6 @@ static void lv_refr_task(void * param)
         uint8_t * buf_act = (uint8_t *) vdb_act->buf;
         uint8_t * buf_ina = (uint8_t *) vdb_ina->buf;
 
-        while(lv_vdb_is_flushing());
-
         uint16_t a;
         for(a = 0; a < inv_buf_p; a++) {
             if(inv_buf[a].joined == 0) {