scc_pata: store 'hwif' pointer in struct scc_ports

Replace 'unsigned char hwif_id' by 'ide_hwif_t *hwif' in struct scc_ports.
This allows us to remove ide_hwifs[] usage from scc_remove().

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>