Make osi_GetTime work on 64-bit libuafs

Make osi_GetTime work on 64-bit libuafs

libuafs was previously using an implementation of osi_GetTime (and
thus clock_GetTime) that required 32-bit time_t's to work properly.
Instead, just use the non-kernel osi_GetTime for UKERNEL, since we're
just in userspace either way.

Change-Id: I4f2d060f7e2aaeaaa3fe164aca6bee5333de4583
Reviewed-on: http://gerrit.openafs.org/1714
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>