Add a counter to keep track of the number of WQs connected to a CQ and
return an error if destroy_cq() is called while the counter is non zero.

Link: https://lore.kernel.org/r/20220421014042.26985-8-rpearsonhpe@gmail.comSigned-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>