RDMA/cxgb4: Remove kref accounting for sync operation

Ucontext allocation and release aren't async events and don't need kref
accounting. The common layer of RDMA subsystem ensures that dealloc
ucontext will be called after all other objects are released.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Tested-by: Raju Rangoju <rajur@chelsio.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>