Documentation/infiniband: update name of some functions

Update the document since those functions had been renamed in below.

Fixes: 0a18cfe4 ("IB/core: Rename ib_create_ah to rdma_create_ah")
Fixes: 67b985b6 ("IB/core: Rename ib_modify_ah to rdma_modify_ah")
Fixes: bfbfd661 ("IB/core: Rename ib_query_ah to rdma_query_ah")
Fixes: 36523159 ("IB/core: Rename ib_destroy_ah to rdma_destroy_ah")
Link: https://lore.kernel.org/r/20190903124519.28318-1-guoqing.jiang@cloud.ionos.com


Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>