.mailmap: specify spelling for Nian Wu

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1999>
diff --git a/.mailmap b/.mailmap
index f245633..009d3e6 100644
--- a/.mailmap
+++ b/.mailmap
@@ -437,6 +437,7 @@
 
 Neil Roberts <nroberts@igalia.com> <neil@linux.intel.com>
 
+Nian Wu <nian.wu@intel.com>
 Nian Wu <nian.wu@intel.com> <nian@graphics.(none)>
 Nian Wu <nian.wu@intel.com> <nian@tinderbox.sh.intel.com>