.mailmap: Update Paul Burton email address

.mailmap: Update Paul Burton email address

Following the Linux kernel equivalent patch posted on
[email protected] [*], update Paul Burton email
address to avoid emails bouncing.

[*] 'MAINTAINERS: Use @kernel.org address for Paul Burton'
https://lore.kernel.org/patchwork/patch/1140341/

Cc: Paul Burton <[email protected]>
Suggested-by: Paolo Bonzini <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Acked-by: Paul Burton <[email protected]>
Message-Id: <20200707022544[email protected]>
Signed-off-by: Laurent Vivier <[email protected]>