MAINTAINERS: add slimbus documentation

In the commit 202318d3
slimbus documentation was added but it missed
the update in this file. Currently get_maintainer script
is missing the main maintainer.

Signed-off-by: anish kumar <yesanishhere@gmail.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20241230143354.266154-3-srinivas.kandagatla@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>