net: atm: fix update of position index in lec_seq_next

The position index in leq_seq_next is not updated when the next
entry is fetched an no more entries are available. This causes
seq_file to report the following error:

"seq_file: buggy .next function lec_seq_next [lec] did not update
 position index"

Fix this by always updating the position index.

[ Note: this is an ancient 2002 bug, the sha is from the
  tglx/history repo ]

Fixes 4aea2cbf ("[ATM]: Move lan seq_file ops to lec.c [1/3]")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20201027114925.21843-1-colin.king@canonical.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/atm/lec.c

@@ -954,9 +954,8 @@ static void *lec_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
 	struct lec_state *state = seq->private;
 
-	v = lec_get_idx(state, 1);
-	*pos += !!PTR_ERR(v);
-	return v;
+	++*pos;
+	return lec_get_idx(state, 1);
 }
 
 static int lec_seq_show(struct seq_file *seq, void *v)