Add MAINTAINERS entry for IOC3 serial driver

The IOC3 is a multifunction device but not in sense of the PCI
specification.  Currently its ethernet and serial functionality are
supported by two separate drivers authored and maintained by different
people, so MAINTAINERS should reflect that.

Cc: Patrick Gefre <pfg@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>