btrfs: ioctl: Try to use btrfs_fs_info instead of *file

Some functions are doing some unnecessary indirection to reach the
btrfs_fs_info struct. Change these functions to receive a btrfs_fs_info
struct instead of a *file.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>