debug/trace: Fix length issue found in compilation

Change-Id: I1cd7fd6464d0912294009c2293ed70f3f6744930
BUG: 1092196
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/7586
Reviewed-by: Anand Avati <avati@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>