hypfs_kill_super(): deal with failed allocations

hypfs_fill_super() might fail to allocate sbi; hypfs_kill_super()
should not oops on that.

Cc: stable@vger.kernel.org
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

arch/s390/hypfs/inode.c

@@ -320,7 +320,7 @@ static void hypfs_kill_super(struct super_block *sb)
 
 	if (sb->s_root)
 		hypfs_delete_tree(sb->s_root);
-	if (sb_info->update_file)
+	if (sb_info && sb_info->update_file)
 		hypfs_remove(sb_info->update_file);
 	kfree(sb->s_fs_info);
 	sb->s_fs_info = NULL;