drivers/net/arcnet: fix sparse warning: symbol shadows an earlier one

Impact: Remove redundant inner scope variable.

Fix this sparse warning:
  drivers/net/arcnet/arcnet.c:383:21: warning: symbol 'count' shadows an earlier one
  drivers/net/arcnet/arcnet.c:375:13: originally declared here

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: David S. Miller <davem@davemloft.net>