MAINTAINERS: Update SHARED MEMORY COMMUNICATIONS (SMC) maintainer entries

MAINTAINERS: Update SHARED MEMORY COMMUNICATIONS (SMC) maintainer entries

Due to a change in responsibilities, I can no longer serve as an SMC
maintainer and need to be removed from the MAINTAINERS list.

To reflect these organizational changes, promote Mahanta Jambigi
<mjambigi@linux.ibm.com> from reviewer to maintainer.

Acked-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Signed-off-by: Wenjia Zhang <wenjia@linux.ibm.com>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://patch.msgid.link/20260724053752.3084-1-wenjia@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>