bpf: make an argument const in the bpf_map_sum_elem_count kfunc

We use the map pointer only to read the counter values, no locking
involved, so mark the argument as const.
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Link: https://lore.kernel.org/r/20230719092952.41202-4-aspsk@isovalent.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/map_iter.c

@@ -197,7 +197,7 @@ __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
 
-__bpf_kfunc s64 bpf_map_sum_elem_count(struct bpf_map *map)
+__bpf_kfunc s64 bpf_map_sum_elem_count(const struct bpf_map *map)
 {
 	s64 *pcount;
 	s64 ret = 0;