RDMA/core: Free DIM memory in error unwind

The memory allocated for the DIM wasn't freed in in error unwind path, fix
it by calling to rdma_dim_destroy().

Fixes: da662979

 ("RDMA/core: Provide RDMA DIM support for ULPs")
Link: https://lore.kernel.org/r/20200730082719.1582397-4-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Max Gurtovoy &lt;maxg@mellanox.com <mailto:maxg@mellanox.com&gt;>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>