.mailmap: specify spelling for Randy Xu

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1999>
diff --git a/.mailmap b/.mailmap
index 5482179..91ed4b2 100644
--- a/.mailmap
+++ b/.mailmap
@@ -491,6 +491,8 @@
 
 Quentin Glidic <sardemff7+git@sardemff7.net> <sardemff7@sardemff7.net>
 
+Randy Xu <randy.xu@intel.com>
+
 RALOVICH, Kristóf <tade60@freemail.hu> <kristof.ralovich@gmail.com>
 
 Richard Li <richardradeon@gmail.com> <RichardZ.Li@amd.com>