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

Impact: Rename inner scrope variable.

Fix this sparse warning:
  drivers/net/hamradio/yam.c:856:35: warning: symbol 'dev' shadows an earlier one

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