qemu.tests.cfg: Update iommu value in sr_iov.cfg

Cause Property 'pci-assign.iommu' doesn't take value '0'.
Signed-off-by: NShuping Cui <scui@redhat.com>

qemu/tests/cfg/sr_iov.cfg

@@ -88,9 +88,9 @@
             variants:
                 - vf_iommu_off:
                     start_vm = no
-                    negative_msg = "\'pci-assign\' could not be initialized"
+                    negative_msg = "'pci-assign' could not be initialized"
                     pci-assign_params = iommu
-                    iommu = 0
+                    iommu = off
                     type = sr_iov_boot_negative
                 - no-kvm:
                     pci_assignable = vf
@@ -110,7 +110,7 @@
                     type = sr_iov_hotplug_negative
                     negative_msg = "Device 'pci-assign' could not be initialized"
                     hotplug_params = iommu
-                    iommu = 0
+                    iommu = off
                 - more_than_max_vfs:
                     driver_option = "max_vfs=8"
                     type = boot