Minor fix - make sure not to call ohci/uhci_init from irq handler.

When CONFIG_THREAD_OPTIONROMS is enabled, accessing the PCI config
space from a thread could potentially race with an option rom.  Make
sure the ohci/uhci_init() functions (which access PCI config space)
are never run while an optionrom could also be running.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/src/usb-ehci.c b/src/usb-ehci.c
index d60465e..5028c0d 100644
--- a/src/usb-ehci.c
+++ b/src/usb-ehci.c
@@ -50,6 +50,10 @@
         struct pci_device *pci = cntl->companion[i];
         if (!pci)
+        // ohci/uhci_init call pci_config_XXX - don't run from irq handler.
+        wait_preempt();
         if (pci_classprog(pci) == PCI_CLASS_SERIAL_USB_UHCI)
             uhci_init(pci, cntl->usb.busid + i);
         else if (pci_classprog(pci) == PCI_CLASS_SERIAL_USB_OHCI)