bpf: add missing percpu_counter_destroy() in htab_map_alloc()

syzbot is reporting ODEBUG bug in htab_map_alloc() [1], for
commit 86fe28f7 ("bpf: Optimize element count in non-preallocated
hash map.") added percpu_counter_init() to htab_map_alloc() but forgot to
add percpu_counter_destroy() to the error path.

Link: https://syzkaller.appspot.com/bug?extid=5d1da78b375c3b5e6c2b [1]
Reported-by: syzbot <syzbot+5d1da78b375c3b5e6c2b@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 86fe28f7 ("bpf: Optimize element count in non-preallocated hash map.")
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/e2e4cc0e-9d36-4ca1-9bfa-ce23e6f8310b@I-love.SAKURA.ne.jpSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/hashtab.c

@@ -622,6 +622,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 free_prealloc:
 	prealloc_destroy(htab);
 free_map_locked:
+	if (htab->use_percpu_counter)
+		percpu_counter_destroy(&htab->pcount);
 	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
 		free_percpu(htab->map_locked[i]);
 	bpf_map_area_free(htab->buckets);