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>

net/appletalk/ddp.c

@@ -1877,7 +1877,7 @@ EXPORT_SYMBOL(aarp_send_ddp);
 EXPORT_SYMBOL(atrtr_get_dev);
 EXPORT_SYMBOL(atalk_find_dev_addr);
 
-static char atalk_err_snap[] __initdata =
+static const char atalk_err_snap[] __initconst =
 	KERN_CRIT "Unable to register DDP with SNAP.\n";
 
 /* Called by proto.c on kernel start up */