MDEV-21452 fixup: recursive recv_sys.mutex lock

In commit 38fd7b7d (MDEV-21452),
2 of the 3 callers of recv_sys.set_corrupt_fs() are already holding
recv_sys.mutex.

storage/innobase/fil/fil0fil.cc

@@ -3028,7 +3028,11 @@ void fil_aio_callback(const IORequest &request)
     if (dberr_t err= buf_page_read_complete(request.bpage, *request.node))
     {
       if (recv_recovery_is_on() && !srv_force_recovery)
+      {
+        mysql_mutex_lock(&recv_sys.mutex);
         recv_sys.set_corrupt_fs();
+        mysql_mutex_unlock(&recv_sys.mutex);
+      }
 
       ib::error() << "Failed to read page " << id.page_no()
                   << " from file '" << request.node->name << "': " << err;

storage/innobase/log/log0recv.cc

@@ -2497,10 +2497,9 @@ ATTRIBUTE_COLD void recv_sys_t::set_corrupt_log()
 
 ATTRIBUTE_COLD void recv_sys_t::set_corrupt_fs()
 {
-  mysql_mutex_lock(&mutex);
+  mysql_mutex_assert_owner(&mutex);
   found_corrupt_fs= true;
   pthread_cond_broadcast(&cond);
-  mysql_mutex_unlock(&mutex);
 }
 
 /** Apply any buffered redo log to a page that was just read from a data file.