Fix up GFP_ZONEMASK for GFP_DMA32 usage

There was some confusion about the different zone usage, this should fix
up the resulting mess in the GFP zonemask handling.

The different zone usage is still confusing (it's very easy to mix up
the individual zone numbers with the GFP zone _list_ numbers), so we
might want to clean up some of this in the future, but in the meantime
this should fix the actual problems.

Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>