[libata] revert new check-ready Status register logic

[libata] revert new check-ready Status register logic

This behavior differs across multiple controllers, so we cannot use
common logic for all controllers.

Revert back to the basic common behavior, and specific drivers will
be updated from here to take into account the unusual Status return
values.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>