bfd: Use ERR_PTR and such instead of BREADERR

No need to invent new error codes here, simply
use ERR_PTR/IS_ERR_OR_NULL and such.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>