test-usb-hub-qemu: spawn proof via descriptor-read line

The 'USB HUB driver spawned' log line is emitted before setup_logging
and never reaches the serial console, so check #2 could never pass.
Use the hub-descriptor read line (emitted only after XhciClientHandle
open + 8-port descriptor fetch succeed) as the spawn proof, and fold
the old duplicate descriptor check into it.

local/scripts/test-usb-hub-qemu.sh

@@ -136,17 +136,13 @@ if [[ "$check_mode" -eq 1 ]]; then
         exit 1
     fi
 
-    # 2. usbhubd spawned for the hub device.
-    if ! grep -q "USB HUB driver spawned" "$log_file"; then
-        echo "ERROR: usbhubd did not spawn for the QEMU usb-hub" >&2
-        echo "       Expected: 'USB HUB driver spawned'" >&2
-        echo "       See $log_file" >&2
-        exit 1
-    fi
-
-    # 3. Hub descriptor read succeeded (QEMU usb-hub exposes 8 ports).
+    # 2. usbhubd spawned for the hub device. The "USB HUB driver spawned"
+    #    log line is emitted before setup_logging and never reaches the
+    #    serial console, so the reliable spawn proof is the hub-descriptor
+    #    read line (emitted only after XhciClientHandle open + descriptor
+    #    fetch succeed).
     if ! grep -q "usbhubd: 8 port(s) detected" "$log_file"; then
-        echo "ERROR: hub descriptor read failed or wrong port count" >&2
+        echo "ERROR: usbhubd did not spawn or hub descriptor read failed" >&2
         echo "       Expected: 'usbhubd: 8 port(s) detected'" >&2
         grep -i "usbhubd" "$log_file" | tail -10 >&2 || true
         echo "       See $log_file" >&2