[IA64-SGI] sn_dma_alloc_coherent should use gfp flags

Takashi helped us track down a bad page state bug we thought was coming
from alsa.  It turns out we weren't paying attention to the gfp flags
that were passed in to sn_dma_alloc_coherent().

From: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Edwards <edwardsg@sgi.com>
Signed-off-by: Mark Maule <maule@sgi.com>
Signed-off-by: Jes Sorensen <jes@sgi.com>