RDMA/hfi1: Convert from atomic_t to refcount_t on hfi1_devdata->user_refcount

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Link: https://lore.kernel.org/r/1626674454-56075-1-git-send-email-xiyuyang19@fudan.edu.cn


Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Tested-by: Josh Fisher <josh.fisher@cornelisnetworks.com>
Acked-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>