MAINTAINERS: eth: mark IBM eHEA as an Orphan

Current maintainer Douglas Miller has left IBM and no replacement has
been assigned for the driver. The eHEA hardware was last used on
IBM POWER7 systems, the last of which reached end-of-support at the
end of 2020.

Signed-off-by: David Christensen <drc@linux.ibm.com>
Reviewed-by: Pradeep Satyanarayana <pradeeps@linux.ibm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Link: https://lore.kernel.org/r/20240418195517.528577-1-drc@linux.ibm.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>