call-stub: remove fall-through in ftruncate

Change-Id: I58bf6b881ff63d627051bef1ab30bd0337ab65e2
BUG: 913544
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/4564
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>