sata_via: restore vt*_prepare_host error handling

commit b9d5b89b (sata_via: fix support
for 5287) accidently (?) removed vt*_prepare_host error handling - restore it

catched by gcc:
drivers/ata/sata_via.c: In function 'svia_init_one':
drivers/ata/sata_via.c:567: warning: 'host' may be used uninitialized in this function

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Joseph Chan <JosephChan@via.com.tw>
Cc: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>