RDMA/siw: Release xarray entry

The xarray entry is allocated in siw_qp_add(), but release was
missed in case zero-sized SQ was discovered.

Fixes: 661f3859 ("RDMA/siw: Fix handling of zero-sized Read and Receive Queues.")
Link: https://lore.kernel.org/r/f070b59d5a1114d5a4e830346755c2b3f141cde5.1620560472.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>