ALSA: memalloc: don't pass bogus GFP_ flags to dma_alloc_*

dma_alloc_coherent/dma_alloc_wc is an opaque allocator that only uses
the GFP_ flags for allocation context control.  Don't pass __GFP_COMP
which makes no sense for an allocation that can't in any way be
converted to a page pointer.

Note that for dma_alloc_noncoherent and dma_alloc_noncontigous in
combination with the DMA mmap helpers __GFP_COMP looks sketchy as well,
so I would suggest to drop that as well after a careful audit.

Signed-off-by: Christoph Hellwig <hch@lst.de>