Cast MSB part of current TSF to u64 to prevent loss of most
significant bits. MSB should also be shifted by 32.

Patch based on old maemo patch by:
Yuri Kululin <ext-yuri.kululin@nokia.com>
Yuri Ershov <ext-yuri.ershov@nokia.com>
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>