MAINTAINERS: transfer maintainership of I/OAT

Dan Williams takes over I/OAT from Maciej Sosnowski

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>