ata: libata-core: Check errors in sata_print_link_status()

sata_scr_read() could return negative error code on failure. Check the
return value when reading the control register.

Signed-off-by: Li Zhong <floridsleeves@gmail.com>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>