hugetlbfs: fix memory leak for resv_map

euler inclusion
category: bugfix
bugzilla: 10984
CVE: NA
---------------------------

When .mknod create a block device file in hugetlbfs, it will
allocate an inode, and kmalloc a 'struct resv_map' in resv_map_alloc().
For now, inode->i_mapping->private_data is used to point the resv_map.
However, when open the device, bd_acquire() will set i_mapping as
bd_inode->imapping, result in resv_map memory leak.

We fix the leak by adding a new entry resv_map in hugetlbfs_inode_info.
It can store resv_map pointer.

Programs to reproduce:
	mount -t hugetlbfs nodev hugetlbfs
	mknod hugetlbfs/dev b 0 0
	exec 30<> hugetlbfs/dev
	umount hugetlbfs/

Fixes: 9119a41e ("mm, hugetlb: unify region structure handling")
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Reviewed-by: Miao Xie <miaoxie@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>