The function isn't implemented - delete the declaration.

Fixes: a9d2e9ae ("RDMA/siw,rxe: Make emulated devices virtual in the device tree")
Link: https://lore.kernel.org/r/20210331102043.691950-1-kamalheib1@gmail.comSigned-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>