iommu/dma: fix variable 'cookie' set but not used

iommu/dma: fix variable 'cookie' set but not used

[ Upstream commit 55817b340a31951d23d1692db45522560b1d20f9 ]

The commit c18647900ec8 ("iommu/dma: Relax locking in
iommu_dma_prepare_msi()") introduced a compliation warning,

drivers/iommu/dma-iommu.c: In function 'iommu_dma_prepare_msi':
drivers/iommu/dma-iommu.c:1206:27: warning: variable 'cookie' set but
not used [-Wunused-but-set-variable]
  struct iommu_dma_cookie *cookie;
                           ^~~~~~

Fixes: c18647900ec8 ("iommu/dma: Relax locking in iommu_dma_prepare_msi()")
Signed-off-by: Qian Cai <cai@lca.pw>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>