appletalk: fix warning: format not a string literal and no ...

Impact: Use 'static const char[]' instead of 'static char[]', and
since the data is const now it can be placed in __initconst.

Fix this warning:
  net/appletalk/ddp.c: In function 'atalk_init':
  net/appletalk/ddp.c:1894: 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>