fdc: fix drive property handling.

Fix the floppy controller init wrappers to set the drive properties
only in case the DriveInfo pointers passed in are non NULL.  This allows
to set the properties using -global.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
(cherry picked from commit 995bf0ca)

hw/fdc.c

@@ -1860,8 +1860,12 @@ fdctrl_t *fdctrl_init_isa(DriveInfo **fds)
     ISADevice *dev;
 
     dev = isa_create("isa-fdc");
-    qdev_prop_set_drive(&dev->qdev, "driveA", fds[0]);
-    qdev_prop_set_drive(&dev->qdev, "driveB", fds[1]);
+    if (fds[0]) {
+        qdev_prop_set_drive(&dev->qdev, "driveA", fds[0]);
+    }
+    if (fds[1]) {
+        qdev_prop_set_drive(&dev->qdev, "driveB", fds[1]);
+    }
     if (qdev_init(&dev->qdev) < 0)
         return NULL;
     return &(DO_UPCAST(fdctrl_isabus_t, busdev, dev)->state);
@@ -1879,8 +1883,12 @@ fdctrl_t *fdctrl_init_sysbus(qemu_irq irq, int dma_chann,
     sys = DO_UPCAST(fdctrl_sysbus_t, busdev.qdev, dev);
     fdctrl = &sys->state;
     fdctrl->dma_chann = dma_chann; /* FIXME */
-    qdev_prop_set_drive(dev, "driveA", fds[0]);
-    qdev_prop_set_drive(dev, "driveB", fds[1]);
+    if (fds[0]) {
+        qdev_prop_set_drive(dev, "driveA", fds[0]);
+    }
+    if (fds[1]) {
+        qdev_prop_set_drive(dev, "driveB", fds[1]);
+    }
     qdev_init_nofail(dev);
     sysbus_connect_irq(&sys->busdev, 0, irq);
     sysbus_mmio_map(&sys->busdev, 0, mmio_base);
@@ -1896,7 +1904,9 @@ fdctrl_t *sun4m_fdctrl_init (qemu_irq irq, target_phys_addr_t io_base,
     fdctrl_t *fdctrl;
 
     dev = qdev_create(NULL, "SUNW,fdtwo");
-    qdev_prop_set_drive(dev, "drive", fds[0]);
+    if (fds[0]) {
+        qdev_prop_set_drive(dev, "drive", fds[0]);
+    }
     qdev_init_nofail(dev);
     sys = DO_UPCAST(fdctrl_sysbus_t, busdev.qdev, dev);
     fdctrl = &sys->state;