test/vfio_user: Update QEMU_BIN to use vfio-user-dbfix

This follows e380263b - all CI nodes have been updated to an image
which ships with that particular version of vfio-user QEMU.

Signed-off-by: Michal Berger <michal.berger@intel.com>
Change-Id: I2029f48014868366881790a4e258190e3f83b0d0
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/13894


Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Dong Yi <dongx.yi@intel.com>
Reviewed-by: GangCao <gang.cao@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Tested-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>