fs/ntfs3: Fix memory leak if ntfs_read_mft failed

In the Linux kernel, the following vulnerability has been resolved:

fs/ntfs3: Fix memory leak if ntfs_read_mft failed

Label ATTR_ROOT in ntfs_read_mft() sets is_root = true and
ni->ni_flags |= NI_FLAG_DIR, then next attr will goto label ATTR_ALLOC
and alloc ni->dir.alloc_run. However two states are not always
consistent and can make memory leak.

1) attr_name in ATTR_ROOT does not fit the condition it will set
is_root = true but NI_FLAG_DIR is not set.
2) next attr_name in ATTR_ALLOC fits the condition and alloc
ni->dir.alloc_run
3) in cleanup function ni_clear(), when NI_FLAG_DIR is set, it frees
ni->dir.alloc_run, otherwise it frees ni->file.run
4) because NI_FLAG_DIR is not set in this case, ni->dir.alloc_run is
leaked as kmemleak reported:

unreferenced object 0xffff888003bc5480 (size 64):
backtrace:
[<000000003d42e6b0>] __kmalloc_node+0x4e/0x1c0
[<00000000d8e19b8a>] kvmalloc_node+0x39/0x1f0
[<00000000fc3eb5b8>] run_add_entry+0x18a/0xa40 [ntfs3]
[<0000000011c9f978>] run_unpack+0x75d/0x8e0 [ntfs3]
[<00000000e7cf1819>] run_unpack_ex+0xbc/0x500 [ntfs3]
[<00000000bbf0a43d>] ntfs_iget5+0xb25/0x2dd0 [ntfs3]
[<00000000a6e50693>] ntfs_fill_super+0x218d/0x3580 [ntfs3]
[<00000000b9170608>] get_tree_bdev+0x3fb/0x710
[<000000004833798a>] vfs_get_tree+0x8e/0x280
[<000000006e20b8e6>] path_mount+0xf3c/0x1930
[<000000007bf15a5f>] do_mount+0xf3/0x110
...

Fix this by always setting is_root and NI_FLAG_DIR together.