btrfs: cleanup duplicated parameters related to create_io_em()
Most parameters of create_io_em() can be replaced by the members with
the same name inside btrfs_file_extent.
Do a direct parameters cleanup here.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>