.mailmap: use correct email address

Signed-off-by: David Heidelberg <david@ixit.cz>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3190>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3190>
diff --git a/.mailmap b/.mailmap
index ded6258..7f0a3fb 100644
--- a/.mailmap
+++ b/.mailmap
@@ -133,8 +133,8 @@
 David Miller <davem@davemloft.net> Dave Miller <davem@davemloft.net>
 David Miller <davem@davemloft.net> davem69 <davem69>
 
-David Heidelberger <david.heidelberger@ixit.cz> David Heidelberg <david@ixit.cz>
-David Heidelberger <david.heidelberger@ixit.cz> <d.okias@gmail.com>
+David Heidelberg <david@ixit.cz> David Heidelberger <david.heidelberger@ixit.cz>
+David Heidelberg <david@ixit.cz> <d.okias@gmail.com>
 
 David Reveman <reveman@chromium.org> <c99drn@cs.umu.se>