netfs: Mark __nonstring lookup tables

GCC 15's new -Wunterminated-string-initialization notices that the
character lookup tables "fscache_cache_states" and "fscache_cookie_states"
(which are not used as a C-String) need to be marked as "nonstring":

fs/netfs/fscache_cache.c:375:67: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (6 chars into 5 available) [-Wunterminated-string-initialization]
  375 | static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW";
      |                                                                   ^~~~~~~
fs/netfs/fscache_cookie.c:32:69: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (11 chars into 10 available) [-Wunterminated-string-initialization]
   32 | static const char fscache_cookie_states[FSCACHE_COOKIE_STATE__NR] = "-LCAIFUWRD";
      |                                                                     ^~~~~~~~~~~~

Annotate the arrays.

Signed-off-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/20250416221654.work.028-kees@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/netfs/fscache_cache.c

@@ -372,7 +372,7 @@ void fscache_withdraw_cache(struct fscache_cache *cache)
 EXPORT_SYMBOL(fscache_withdraw_cache);
 
 #ifdef CONFIG_PROC_FS
-static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW";
+static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] __nonstring = "-PAEW";
 
 /*
  * Generate a list of caches in /proc/fs/fscache/caches

fs/netfs/fscache_cookie.c

@@ -29,7 +29,7 @@ static LIST_HEAD(fscache_cookie_lru);
 static DEFINE_SPINLOCK(fscache_cookie_lru_lock);
 DEFINE_TIMER(fscache_cookie_lru_timer, fscache_cookie_lru_timed_out);
 static DECLARE_WORK(fscache_cookie_lru_work, fscache_cookie_lru_worker);
-static const char fscache_cookie_states[FSCACHE_COOKIE_STATE__NR] = "-LCAIFUWRD";
+static const char fscache_cookie_states[FSCACHE_COOKIE_STATE__NR] __nonstring = "-LCAIFUWRD";
 static unsigned int fscache_lru_cookie_timeout = 10 * HZ;
 
 void fscache_print_cookie(struct fscache_cookie *cookie, char prefix)