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

Impact: Rename a local variable resp. remove a redundant variable and
while being at it use more unform loop constructs.

Fix this sparse warning:
  drivers/net/tulip/de4x5.c:3944:13: warning: symbol 'i' shadows an earlier one
  drivers/net/tulip/de4x5.c:3938:9: originally declared here
  drivers/net/tulip/media.c:72:21: warning: symbol 'i' shadows an earlier one
  drivers/net/tulip/media.c:54:13: originally declared here
  drivers/net/tulip/media.c:134:21: warning: symbol 'i' shadows an earlier one
  drivers/net/tulip/media.c:117:13: originally declared here

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