m68k/atari - ataflop: use correct virt/phys translation for DMA buffer

With the kernel running from FastRAM instead of ST-RAM, none of ST-RAM is
mapped by mem_init, and DMA-addressable buffer must be mapped by ioremap.

Use platform specific virt/phys translation helpers for this case.

Signed-off-by: Michael Schmitz <[e-mail]>
Cc: [e-mail]
Signed-off-by: Geert Uytterhoeven <[e-mail]>

drivers/block/ataflop.c

···
 		goto Enomem;
 	}
 	TrackBuffer = DMABuffer + 512;
-	PhysDMABuffer = virt_to_phys(DMABuffer);
+	PhysDMABuffer = atari_stram_to_phys(DMABuffer);
 	PhysTrackBuffer = virt_to_phys(TrackBuffer);
 	BufferDrive = BufferSide = BufferTrack = -1;