decnet: fix sparse warnings: symbol shadows an earlier one

Impact: Remove redundant variable declarations, resp. rename
inner scope variable.

Fix this sparse warnings:
  net/decnet/af_decnet.c:1252:40: warning: symbol 'skb' shadows an earlier one
  net/decnet/af_decnet.c:1223:24: originally declared here
  net/decnet/af_decnet.c:1582:29: warning: symbol 'val' shadows an earlier one
  net/decnet/af_decnet.c:1527:22: originally declared here
  net/decnet/dn_dev.c:687:21: warning: symbol 'err' shadows an earlier one
  net/decnet/dn_dev.c:670:13: originally declared here
  net/decnet/sysctl_net_decnet.c:182:21: warning: symbol 'len' shadows an earlier one
  net/decnet/sysctl_net_decnet.c:173:16: originally declared here

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/decnet/sysctl_net_decnet.c b/net/decnet/sysctl_net_decnet.c
index 965397a..5bcd592 100644
--- a/net/decnet/sysctl_net_decnet.c
+++ b/net/decnet/sysctl_net_decnet.c
@@ -179,7 +179,7 @@
 	}
 
 	if (write) {
-		int len = (*lenp < DN_ASCBUF_LEN) ? *lenp : (DN_ASCBUF_LEN-1);
+		len = (*lenp < DN_ASCBUF_LEN) ? *lenp : (DN_ASCBUF_LEN-1);
 
 		if (copy_from_user(addr, buffer, len))
 			return -EFAULT;