MAINTAINERS: Remove myself as cxl maintainer

I am no longer employed by IBM and will no longer have access to cxl
hardware, so remove myself as a cxl maintainer.

If anyone needs to contact me in the future, please use my personal
email address darkstarsword@gmail.com

Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Cc: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Cc: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>