RDMA: Restore ability to return error for destroy WQ

Make this interface symmetrical to other destroy paths.

Fixes: a49b1dc7 ("RDMA: Convert destroy_wq to be void")
Link: https://lore.kernel.org/r/20200907120921.476363-9-leon@kernel.org


Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>