ata: libata-sff: use *switch* statement in ata_sff_dev_classify()

In ata_sff_dev_classify(), replace a string of the *if* statements checking
the device's class with the *switch* statement that fits better here...

While at it, fix the multi-line comment style in the vicinity...

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