Use list_last_entry and list_first_entry instead of using prev and next
pointers.

Link: https://lore.kernel.org/r/20210608211415.680-1-shiraz.saleem@intel.comReported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>