.mailmap: specify spelling for Sonny Jiang

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1999>
diff --git a/.mailmap b/.mailmap
index a71ad44..96127c8 100644
--- a/.mailmap
+++ b/.mailmap
@@ -542,6 +542,8 @@
 
 Sinclair Yeh <syeh@vmware.com> <sinclair.yeh@intel.com>
 
+Sonny Jiang <sonny.jiang@amd.com>
+
 Stefan Brüns <stefan.bruens@rwth-aachen.de> <Stefan.Bruens@rwth-aachen.de>
 
 Stéphane Marchesin <marcheu@chromium.org> Stephane Marchesin <marchesin@icps.u-strasbg.fr>