MAINTAINERS: add entry for auxiliary bus

MAINTAINERS: add entry for auxiliary bus

When auxiliary bus was added to the kernel the MAINTAINERS file wasn't
updated with a mention of the files, contributors and reviewers. Fix
that oversight by adding Dave and Ira, with GregKH as (same as current)
owner.

CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: Dave Ertman <david.m.ertman@intel.com>
Acked-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20230511164501.3859674-1-jesse.brandeburg@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>