util: Update kdev_to_odev to respect BITS_PER_LONG

Depending on BITS_PER_LONG userspace representation of dev_t
may vary, so we need to choose proper encoding.

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