nvme-pci: don't use dma_alloc_noncontiguous with 0 merge boundary

nvme-pci: don't use dma_alloc_noncontiguous with 0 merge boundary

Only call into nvme_alloc_host_mem_single which uses
dma_alloc_noncontiguous when there is non-null dma merge boundary.
Without this we'll call into dma_alloc_noncontiguous for device using
dma-direct, which can work fine as long as the preferred size is below the
MAX_ORDER of the page allocator, but blows up with a warning if it is
too large.

Fixes: 63a5c7a4b4c4 ("nvme-pci: use dma_alloc_noncontigous if possible")
Reported-by: Leon Romanovsky <leon@kernel.org>
Reported-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Leon Romanovsky <leon@kernel.org>
Tested-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>