selftest/bpf/benchs: Make a function static in bpf_hashmap_full_update

The hashmap_report_final callback function defined in the
benchs/bench_bpf_hashmap_full_update.c file should be static.

Signed-off-by: Anton Protopopov <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/benchs/bench_bpf_hashmap_full_update.c

···
 		bpf_map_update_elem(map_fd, &i, &i, BPF_ANY);
 }
 
-void hashmap_report_final(struct bench_res res[], int res_cnt)
+static void hashmap_report_final(struct bench_res res[], int res_cnt)
 {
 	unsigned int nr_cpus = bpf_num_possible_cpus();
 	int i;