ALSA: memalloc: remove snd_dma_sg_ops declaration

snd_dma_sg_ops has been removed since
commit 2c95b92e ("ALSA: memalloc: Unify x86 SG-buffer handling
(take#3)"), so remove it.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Link: https://lore.kernel.org/r/20220909035443.1065737-3-cuigaosheng1@huawei.com


Signed-off-by: Takashi Iwai <tiwai@suse.de>