ionic: update MAINTAINERS entry

Now that Pensando is a part of AMD we need to update
a couple of addresses.  We're keeping the mailing list
address for the moment, but that will likely change in
the near future.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Link: https://lore.kernel.org/r/20221129011734.20849-1-shannon.nelson@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>