swiotlb: suppress warning when __GFP_NOWARN is set

TTM tries to allocate coherent memory in chunks of 2MB first to improve
TLB efficiency and falls back to allocating 4K pages if that fails.

Suppress the warning when the 2MB allocations fails since there is a
valid fall back path.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-by: Mike Galbraith <efault@gmx.de>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=104082


CC: stable@vger.kernel.org
Signed-off-by: Christoph Hellwig <hch@lst.de>