libqos: usb-hcd-ehci: use 32-bit write for config register

The memory region ops have min_access_size == 4 so obey it.
Tested-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

tests/qtest/usb-hcd-ehci-test.c

@@ -96,7 +96,7 @@ static void pci_ehci_port_1(void)
 static void pci_ehci_config(void)
 {
     /* hands over all ports from companion uhci to ehci */
-    qpci_io_writew(ehci1.dev, ehci1.bar, 0x60, 1);
+    qpci_io_writel(ehci1.dev, ehci1.bar, 0x60, 1);
 }
 
 static void pci_uhci_port_2(void)