git: disk/fd - fix panics

[Matthias Schmidt]

* Alex wrote:
> This (probably) breaks boot up on my VMWare DragonFly. I get the panic:
> "panic: device_busy: called for unattached device"
> 
> Backtrace is,
> panic
> device_busy (4 times)
> fdstrategy
> dev_dstrategy
> diskstrategy
> dev_dstrategy
> diskstrategy
> dev_dstrategy
> mbrinit
> disk_probe

I can confirm this:
http://leaf.dragonflybsd.org/~matthias/screen-capture.png

Cheers

	Matthias