This is more correct, as if st_dev == phys_dev check fails
we have to treat phys_dev as kdev for path resolve device
comparison.

Howver, this is not the case for non-btrfs FSs, and for the
latter one doesn't change anything as it uses anon devices
which are equal for kdev and odev cases.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>