btrfs-progs: do table lookup for simple RAID profiles' num_stripes
For the two simple "RAID" profiles single and dup, we can simply fallback
to a table lookup to get num_stripes.
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>