RDMA/rdmavt: Fix rvt_create_ah function signature

rdmavt uses a crazy system that looses the type checking when assinging
functions to struct ib_device function pointers. Because of this the
signature to this function was not changed when the below commit revised
things.

Fix the signature so we are not calling a function pointer with a
mismatched signature.

Fixes: 477864c8 ("IB/core: Let create_ah return extended response to user")
Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>