swiotlb: suppress warning when __GFP_NOWARN is set

swiotlb: suppress warning when __GFP_NOWARN is set

BugLink: http://bugs.launchpad.net/bugs/1749202
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>
(cherry picked from commit d0bc0c2a31c95002d37c3cc511ffdcab851b3256)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>