qemu: Fix comparison assignment in qemuDomainUpdateDeviceLive

Fix this common typo and assign a value rather than implicitly
type-casted comparison result. Introduced by commit b6a264e8.
Signed-off-by: NErik Skultety <eskultet@redhat.com>

src/qemu/qemu_driver.c

@@ -7919,7 +7919,7 @@ qemuDomainUpdateDeviceLive(virDomainObjPtr vm,
         break;
 
     case VIR_DOMAIN_DEVICE_GRAPHICS:
-        if ((idx = qemuDomainFindGraphicsIndex(vm->def, dev->data.graphics) >= 0)) {
+        if ((idx = qemuDomainFindGraphicsIndex(vm->def, dev->data.graphics)) >= 0) {
             oldDev.data.graphics = vm->def->graphics[idx];
             if (virDomainDefCompatibleDevice(vm->def, dev, &oldDev) < 0)
                 return -1;