ata: pata_artop: use *switch* in atp8xx_fixup()

This driver uses a string of the *if* statements in atp8xx_fixup() where
a *switch* statement would fit better...

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