RDMA/bnxt_re: Remove unsupported modify_device callback

There is no need to return always zero for function which is not
supported.

Link: https://lore.kernel.org/r/20190923104158.5331-3-kamalheib1@gmail.com


Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>