gdb/tui: Make local variable const.

Small clean up to make a local variable const and remove a cast of NULL.

gdb/ChangeLog:

	* tui/tui-data.c (tui_win_name): Make local variable const, remove
	cast of NULL.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2015-08-31  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* tui/tui-data.c (tui_win_name): Make local variable const, remove
+	cast of NULL.
+
 2015-08-31  Max Filippov  <jcmvbkbc@gmail.com>
 
 	* xtensa-tdep.h (XTENSA_GDBARCH_TDEP_INSTANTIATE): Initialize

gdb/tui/tui-data.c

@@ -402,7 +402,7 @@ tui_partial_win_by_name (char *name)
 const char *
 tui_win_name (const struct tui_gen_win_info *win_info)
 {
-  char *name = (char *) NULL;
+  const char *name = NULL;
 
   switch (win_info->type)
     {