qemuDomainDetachDeviceConfig: Don't free device from @dev

https://bugzilla.redhat.com/show_bug.cgi?id=1591561

For reasons I don't understand my original patch of 75f0fd51
freed not only the chardev from domain but also the one from
passed virDomainDeviceDefPtr. This caused no troubles until now,
because those two pointers were separate, but after I've
introduced virDomainDetachDeviceAlias() they became the same
resulting in double free on detach.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_driver.c

@@ -8241,8 +8241,6 @@ qemuDomainDetachDeviceConfig(virDomainDefPtr vmdef,
             return -1;
 
         virDomainChrDefFree(chr);
-        virDomainChrDefFree(dev->data.chr);
-        dev->data.chr = NULL;
         break;
 
     case VIR_DOMAIN_DEVICE_FS: