driver/qemudriver: fix disk attribute for vexpress-a9 machine

Since the q35 machine was added, using the vexpress-a9 machine with a
disk attribute ends up with a NotImplementedError. Fix that.

Fixes: 9bdacb2 ("driver/qemudriver: add support for Q35 machine")
Signed-off-by: Bastian Krause <bst@pengutronix.de>

Author: Bastian-Krause

labgrid/driver/qemudriver.py

@@ -121,7 +121,7 @@ def on_activate(self):
                 self._cmd.append(
                     f"if=sd,format={disk_format},file={disk_path},id=mmc0")
                 boot_args.append("root=/dev/mmcblk0p1 rootfstype=ext4 rootwait")
-            if self.machine == "q35":
+            elif self.machine == "q35":
                 self._cmd.append("-drive")
                 self._cmd.append(
                     f"if=virtio,format={disk_format},file={disk_path}")