Fix: orig_start removed from btrfs_get_extent in 6.11-rc1

Fix: orig_start removed from btrfs_get_extent in 6.11-rc1

See upstream commit:

    commit 4aa7b5d1784f510c0f42afc1d74efb41947221d7
    Author: Qu Wenruo <wqu@suse.com>
    Date:   Tue Apr 30 07:53:04 2024 +0930

        btrfs: remove extent_map::orig_start member

        Since we have extent_map::offset, the old extent_map::orig_start is just
        extent_map::start - extent_map::offset for non-hole/inline extents.

        And since the new extent_map::offset is already verified by
        validate_extent_map() while the old orig_start is not, let's just remove
        the old member from all call sites.

Change-Id: I025a30d49b3e3ddc37d7846acc191ebbdf2ff19e
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>