mm, mempolicy: silence gcc warning

Fengguang Wu reports that compiling mm/mempolicy.c results in a warning:

  mm/mempolicy.c: In function 'mpol_to_str':
  mm/mempolicy.c:2878:2: error: format not a string literal and no format arguments

Kees says this is because he is using -Wformat-security.

Silence the warning.
Signed-off-by: David Rientjes <rientjes@google.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mempolicy.c

@@ -2950,7 +2950,7 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 		return;
 	}
 
-	p += snprintf(p, maxlen, policy_modes[mode]);
+	p += snprintf(p, maxlen, "%s", policy_modes[mode]);
 
 	if (flags & MPOL_MODE_FLAGS) {
 		p += snprintf(p, buffer + maxlen - p, "=");