x86: fix dma_alloc_pages

memory-less node support:

this patch uses updated dev_to_node, because dev_to_node already makes sure
it returns an online node.

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>