btrfs: zoned: fix stripe width calculation

btrfs: zoned: fix stripe width calculation

The stripe offset calculation in the zoned code for raid0 and raid10
wrongly uses map->stripe_size to calculate it. In fact, map->stripe_size is
the size of the device extent composing the block group, which always is
the zone_size on the zoned setup.

Fix it by using BTRFS_STRIPE_LEN and BTRFS_STRIPE_LEN_SHIFT. Also, optimize
the calculation a bit by doing the common calculation only once.

Fixes: c0d90a79e8e6 ("btrfs: zoned: fix alloc_offset calculation for partly conventional block groups")
CC: stable@vger.kernel.org # 6.17+
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>