ipmr: Fix ptrdiff_t print formatting

ipmr_vif_seq_show() prints the difference between two pointers with the
format string %2zd (z for size_t), however the correct format string is
%2td instead (t for ptrdiff_t).

The same bug in ip6mr_vif_seq_show() was already fixed long ago by
commit d430a227 ("bogus format in ip6mr").
Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipmr.c

@@ -3022,7 +3022,7 @@ static int ipmr_vif_seq_show(struct seq_file *seq, void *v)
 		const char *name =  vif->dev ? vif->dev->name : "none";
 
 		seq_printf(seq,
-			   "%2zd %-10s %8ld %7ld  %8ld %7ld %05X %08X %08X\n",
+			   "%2td %-10s %8ld %7ld  %8ld %7ld %05X %08X %08X\n",
 			   vif - mrt->vif_table,
 			   name, vif->bytes_in, vif->pkt_in,
 			   vif->bytes_out, vif->pkt_out,