test/vhost: Replace error() with simple echo

In this particular case, error() is called before it's declared,
hence bash complains that it's missing, failing to print out the
actual error message.

To not shuffle code around, simply replace this call with an echo
to stderr.

Signed-off-by: Michal Berger <michallinuxstuff@gmail.com>
Change-Id: I6f0a6e5b0dfd6893aee6a66e6efdb9874245fafb
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/12427


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Karol Latecki <karol.latecki@intel.com>