iw_cxgb4: Update Maintainer details

Remove Steve and add undersigned as maintainer for iw_cxgb4 drivers.

Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Acked-by: Steve Wise <larrystevenwise@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>