tviced: Fix serialize_state.o objdir

tviced: Fix serialize_state.o objdir

At least some makes treat ./serialize_state.c as only in the current
dir, ignoring VPATH. So just specify serialize_state.c.

Change-Id: I250886cb4bbfb955984b39c5a7d1a1acd5d9e0c4
Reviewed-on: http://gerrit.openafs.org/2524
Tested-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>