ata: pata_hpt3x2n: drop unused 'struct hpt_chip'

The driver has never used 'struct hpt_chip' -- drop its declaration.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>