drivers/net/tokenring: fix warning: format not a string literal and no ...

Impact: Use 'static const char[]' instead of 'static char[]'.

Fix this warnings:
  drivers/net/tokenring/smctr.c:3644: warning: format not a string literal and no format arguments

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