ntfs3: drop inode references in ntfs_put_super()

Recently we moved most cleanup from ntfs_put_super() into
ntfs3_kill_sb() as part of a bigger cleanup.  This accidently also moved
dropping inode references stashed in ntfs3's sb->s_fs_info from
@sb->put_super() to @sb->kill_sb().  But generic_shutdown_super()
verifies that there are no busy inodes past sb->put_super().  Fix this
and disentangle dropping inode references from freeing @sb->s_fs_info.

Fixes: a4f64a30

 ("ntfs3: free the sbi in ->kill_sb") # mainline only
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>