iommu/arm-smmu: Fix missing unlock on error in arm_smmu_device_group()

Add the missing unlock before return from function arm_smmu_device_group()
in the error handling case.

Fixes: b1a1347 ("iommu/arm-smmu: Fix race condition during iommu_group creation")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210820074949.1946576-1-yangyingliang@huawei.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/arm/arm-smmu/arm-smmu.c

@@ -1488,8 +1488,10 @@ static struct iommu_group *arm_smmu_device_group(struct device *dev)
 	mutex_lock(&smmu->stream_map_mutex);
 	for_each_cfg_sme(cfg, fwspec, i, idx) {
 		if (group && smmu->s2crs[idx].group &&
-		    group != smmu->s2crs[idx].group)
+		    group != smmu->s2crs[idx].group) {
+			mutex_unlock(&smmu->stream_map_mutex);
 			return ERR_PTR(-EINVAL);
+		}
 
 		group = smmu->s2crs[idx].group;
 	}