Revert commit 0555659d from 2.6.22-rc1.
The dma_set_mask call somehow failed on a PowerMac G5, PPC64:
http://lkml.org/lkml/2007/8/1/344

Should there ever occur a DMA mapping beyond the physical DMA range, a
proper SBP-2 firmware will report transport errors.  So let's leave it
at that.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Tested-by: Olaf Hering <olh@suse.de>