MAINTAINERS: mailmap: update Shakeel's email address

Moving to linux.dev based email for kernel work.

Link: https://lkml.kernel.org/r/20240219205050.887810-1-shakeel.butt@linux.dev


Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>