RDMA/rxe: Remove useless EXPORT_SYMBOL

The RXE driver is standalone module and hence doesn't need to export
symbols, nor does this one line function deserve to be not inlined.

Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>