btrfs: pass btrfs_io_geometry to is_single_device_io

Now that we have the stripe tree decision saved in struct
btrfs_io_geometry we can pass it into is_single_device_io() and get rid of
another call to btrfs_need_raid_stripe_tree_update().

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>