MAINTAINERS: net: mlxsw: Remove Jiri as a maintainer, add myself

Jiri has moved on and will not carry out the mlxsw maintainership duty any
longer. Add myself as a co-maintainer instead.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Acked-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/45b54312cdebaf65c5d110b15a5dd2df795bf2be.1638807297.git.petrm@nvidia.com


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