MAINTAINERS: add Jan as DMI/SMBIOS support maintainer

I am familiar with these drivers and I care about them so let me add
myself as their maintainer.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>