iommu/arm-smmu-v3: remove set but not used variable 'smmu'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/iommu/arm-smmu-v3.c:2989:26:
warning: variable ‘smmu’ set but not used [-Wunused-but-set-variable]
  struct arm_smmu_device *smmu;
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NChen Zhou <chenzhou10@huawei.com>
Link: https://lore.kernel.org/r/20200508014955.87630-1-chenzhou10@huawei.comSigned-off-by: NWill Deacon <will@kernel.org>

drivers/iommu/arm-smmu-v3.c

@@ -2986,13 +2986,11 @@ static void arm_smmu_release_device(struct device *dev)
 {
 	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
 	struct arm_smmu_master *master;
-	struct arm_smmu_device *smmu;
 
 	if (!fwspec || fwspec->ops != &arm_smmu_ops)
 		return;
 
 	master = dev_iommu_priv_get(dev);
-	smmu = master->smmu;
 	arm_smmu_detach_dev(master);
 	arm_smmu_disable_pasid(master);
 	kfree(master);