ata: pata_hpt37x: fix PCI clock detection

The f_CNT register (at the PCI config. address 0x78) is 16-bit, not
8-bit! The bug was there from the very start... :-(

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Fixes: 669a5db4 ("[libata] Add a bunch of PATA drivers.")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>