[PATCH] powerpc: make ISA floppies work again

We used to assume that a DMA mapping request with a NULL dev was for
ISA DMA.  This assumption was broken at some point.  Now we explicitly
pass the detected ISA PCI device in the floppy setup.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>