Fix: block_len removed frmo btrfs_get_extent in 6.11-rc1

Fix: block_len removed frmo btrfs_get_extent in 6.11-rc1

See upstream commit:

    commit e28b851ed9b232c3b84cb8d0fedbdfa8ca881386
    Author: Qu Wenruo <wqu@suse.com>
    Date:   Tue Apr 30 07:53:05 2024 +0930

        btrfs: remove extent_map::block_len member

        The extent_map::block_len is either extent_map::len (non-compressed
        extent) or extent_map::disk_num_bytes (compressed extent).

        Since we already have sanity checks to do the cross-checks between the
        new and old members, we can drop the old extent_map::block_len now.

        For most call sites, they can manually select extent_map::len or
        extent_map::disk_num_bytes, since most if not all of them have checked
        if the extent is compressed.

Change-Id: Ib03fc685b4e876bf4e53afdd28ca9826342a0e4e
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>