virtio: bus_id for devices should contain 'virtio'

Chris Lalancette <clalance@redhat.com> points out that virtio.c sets all device
names to '0', '1', etc, which looks silly in /proc/interrupts.  We change this
from '%d' to 'virtio%d'.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Carsten Otte <cotte@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Chris Lalancette <clalance@redhat.com>
Cc: Anthony Liguori <anthony@codemonkey.ws>

drivers/virtio/virtio.c

@@ -166,7 +166,7 @@ int register_virtio_device(struct virtio_device *dev)
 	int err;
 
 	dev->dev.bus = &virtio_bus;
-	sprintf(dev->dev.bus_id, "%u", dev->index);
+	sprintf(dev->dev.bus_id, "virtio%u", dev->index);
 
 	/* We always start by resetting the device, in case a previous
 	 * driver messed it up.  This also tests that code path a little. */