bfd: timerfd -- Fix parsing typo

While been converting reading of data stream
to bfd the @buf member was left untouched leading
to incorrect data to be read, fix it setting up
proper one, ie @str itself, otherwise dumping
of timerfd files are failing.

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