ide: make 'extra' field in struct ide_port_info u8

The maximum value used currently for 'extra' field in struct ide_port_info
is 240.

Make 'extra' u8 so it packs nicely together with enablebits[] and 'chipset'
fields (ide_pci_enablebit_t is 3 bytes and hwif_chipset_t is 1 byte).

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>