LU-14195 obdclass: change list_sort to use const pointers

LU-14195 obdclass: change list_sort to use const pointers

Kernel 5.10.70 commit 4f0f586bf0c898233d8f316f471a21db2abd522d
defines the list_cmp_func_t type and changes the comparison
function types of all list_sort() callers to use const pointers
to avoid type mismatches.

Change-Id: I40d37ec0f0d485d0deebaa9dc3493f2865f76ec9
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/45219
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>