RDMA/uverbs: Fix create WQ to use the given user handle

RDMA/uverbs: Fix create WQ to use the given user handle

Fix create WQ to use the given user handle, in addition dropped some
duplicated code from this flow.

Fixes: fd3c7904db6e ("IB/core: Change idr objects to use the new schema")
Fixes: f213c0527210 ("IB/uverbs: Add WQ support")
Link: https://lore.kernel.org/r/20200506082444.14502-9-leon@kernel.org
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>