ata: make ata_port::fastdrain_cnt *unsigned int*

*unsigned long* ata_port::fastdrain_cnt (64-bit value in a 64-bit kernel)
is always assigned from the 32-bit *unsigned int* variables, thus could
also be made just *unsigned int*...

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