kvm: always pass -usb

This will be the default anyway and it was a mistake to pass it only if
the mouse was specified.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>

lib/hypervisor/hv_kvm.py

@@ -1172,8 +1172,9 @@ class KVMHypervisor(hv_base.BaseHypervisor):
     spice_bind = hvp[constants.HV_KVM_SPICE_BIND]
     spice_ip_version = None
 
+    kvm_cmd.extend(["-usb"])
+
     if mouse_type:
-      kvm_cmd.extend(["-usb"])
       kvm_cmd.extend(["-usbdevice", mouse_type])
     elif vnc_bind_address:
       kvm_cmd.extend(["-usbdevice", constants.HT_MOUSE_TABLET])