btrfs: make btrfs_destroy_marked_extents() return void

Currently btrfs_destroy_marked_extents() is returning the value of the
last call to find_first_extent_bit(), which returns a value of 1 meaning
no more ranges found the dirty pages io tree. This value is useless to the
single caller of btrfs_destroy_marked_extents(), which ignores any return
value from btrfs_destroy_marked_extents(). This is because it's only used
in the transaction abort path, where we can't even deal with any errors
since we are in a critical situation already and cleanup of resources is
done in a best effort fashion.

So make btrfs_destroy_marked_extents() return void.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>