MAINTAINERS: nfc: add Krzysztof Kozlowski as maintainer

The NFC subsystem is orphaned.  I am happy to spend some cycles to
review the patches, send pull requests and in general keep the NFC
subsystem running.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>