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 <[e-mail]>
Reported-by: Fengguang Wu <[e-mail]>
Suggested-by: Kees Cook <[e-mail]>
Acked-by: Kees Cook <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/mempolicy.c

···
 		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, "=");