devpts: Make devpts_kill_sb safe if fsi is NULL

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/devpts/inode.c

@@ -458,7 +458,8 @@ static void devpts_kill_sb(struct super_block *sb)
 {
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
 
-	ida_destroy(&fsi->allocated_ptys);
+	if (fsi)
+		ida_destroy(&fsi->allocated_ptys);
 	kfree(fsi);
 	kill_litter_super(sb);
 }