ata: libata-core: get rid of *else* branches in ata_id_n_sectors()

Using *else* after *return* doesn't make much sense -- getting rid of such
*else* branches reduces the indentation levels and thus reduces # of LoC...

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