hw/usb-ohci.c: Ignore writes to HcPeriodCurrentED register

HcPeriodCurrentED is read-only, but Linux writes to it anyway; silently
ignore this rather than printing a warning message.

(Specifically, drivers/usb/host/ohci-hub.c:ohci_rh_resume() writes a
0, in at least kernels 2.6.25 through 2.6.39.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb-ohci.c

diff --git a/hw/usb-ohci.c b/hw/usb-ohci.c
index 401045a..ab77434 100644
--- a/hw/usb-ohci.c
+++ b/hw/usb-ohci.c
@@ -1575,6 +1575,10 @@
         ohci->hcca = val & OHCI_HCCA_MASK;
         break;
 
+    case 7: /* HcPeriodCurrentED */
+        /* Ignore writes to this read-only register, Linux does them */
+        break;
+
     case 8: /* HcControlHeadED */
         ohci->ctrl_head = val & OHCI_EDPTR_MASK;
         break;