ata: pata_parport-bpck6: remove ppc_id from struct ppc_storage

ppc_id duplicates pi->unit. Remove it.

Signed-off-by: Ondrej Zary <linux@zary.sk>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>