RDMA/bnxt_re: Delete unsupported modify_port function

There is no need to return always zero for function which is not
supported. The IB stack treats uninitialized ib_device->functions as
not implemented.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Acked-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>