rpcsvc/dump: return correct return value

fix e8d09b9ab9 resulted in rpcsvc_dump returning large non-zero
values to caller in case of success. This patch fixes that issue
by returning 0

Change-Id: I594703dada74da17b33c98b073627a3378d170c5
BUG: 903113
Signed-off-by: Raghavendra G <raghavendra@gluster.com>
Reviewed-on: http://review.gluster.org/4477
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>