Remove io_index argument from cpu_register_io_memory()

The parameter is always zero except when registering the three internal
io regions (ROM, unassigned, notdirty).  Remove the parameter to reduce
the API's power, thus facilitating future change.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/hw/xilinx_uartlite.c b/hw/xilinx_uartlite.c
index 5cfb36c..9bf2e91 100644
--- a/hw/xilinx_uartlite.c
+++ b/hw/xilinx_uartlite.c
@@ -201,7 +201,7 @@
     sysbus_init_irq(dev, &s->irq);
 
     uart_update_status(s);
-    uart_regs = cpu_register_io_memory(0, uart_read, uart_write, s);
+    uart_regs = cpu_register_io_memory(uart_read, uart_write, s);
     sysbus_init_mmio(dev, R_MAX * 4, uart_regs);
 
     s->chr = qdev_init_chardev(&dev->qdev);