drivers/isdn: Use static const char * const where possible

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/isdn/pcbit/edss1.c b/drivers/isdn/pcbit/edss1.c
index d5920ae..80c9c16 100644
--- a/drivers/isdn/pcbit/edss1.c
+++ b/drivers/isdn/pcbit/edss1.c
@@ -33,7 +33,7 @@
 #include "callbacks.h"
 
 
-char * isdn_state_table[] = {
+const char * const isdn_state_table[] = {
   "Closed",
   "Call initiated",
   "Overlap sending",