.mailmap: update email address for Christopher Obbard

Update my email address.

Link: https://lkml.kernel.org/r/20250122-wip-obbardc-update-email-v2-1-12bde6b79ad0@linaro.org


Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>