mailmap: update Kirill's email

My new email address is kirill.tkhai@openvz.org.

Link: https://lkml.kernel.org/r/164846762354.278960.13129571556274098855.stgit@pro
Signed-off-by: Kirill Tkhai <kirill.tkhai@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

.mailmap

@@ -213,6 +213,7 @@ Kees Cook <keescook@chromium.org> <kees@ubuntu.com>
 Keith Busch <kbusch@kernel.org> <keith.busch@intel.com>
 Keith Busch <kbusch@kernel.org> <keith.busch@linux.intel.com>
 Kenneth W Chen <kenneth.w.chen@intel.com>
+Kirill Tkhai <kirill.tkhai@openvz.org> <ktkhai@virtuozzo.com>
 Konstantin Khlebnikov <koct9i@gmail.com> <khlebnikov@yandex-team.ru>
 Konstantin Khlebnikov <koct9i@gmail.com> <k.khlebnikov@samsung.com>
 Koushik <raghavendra.koushik@neterion.com>