ide: rename IDE_TFLAG_IN_[HOB_]FEATURE

The feature register has never been readable -- when its location is read, one
gets the error register value; hence rename IDE_TFLAG_IN_[HOB_]FEATURE into
IDE_TFLAG_IN_[HOB_]ERROR and introduce the 'hob_error' field into the 'struct
ide_taskfile' (despite the error register not really depending on the HOB bit).

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>