drm/msm/adreno: fix probe without iommu

The function iommu_domain_alloc returns NULL on platforms without IOMMU
such as msm8974. This resulted in PTR_ERR(-ENODEV) being assigned to
gpu->aspace so the correct code path wasn't taken.

Fixes: ccac7ce3 ("drm/msm: Refactor address space initialization")
Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/adreno_gpu.c

@@ -189,10 +189,16 @@ struct msm_gem_address_space *
 adreno_iommu_create_address_space(struct msm_gpu *gpu,
 		struct platform_device *pdev)
 {
-	struct iommu_domain *iommu = iommu_domain_alloc(&platform_bus_type);
-	struct msm_mmu *mmu = msm_iommu_new(&pdev->dev, iommu);
+	struct iommu_domain *iommu;
+	struct msm_mmu *mmu;
 	struct msm_gem_address_space *aspace;
 
+	iommu = iommu_domain_alloc(&platform_bus_type);
+	if (!iommu)
+		return NULL;
+
+	mmu = msm_iommu_new(&pdev->dev, iommu);
+
 	aspace = msm_gem_address_space_create(mmu, "gpu", SZ_16M,
 		0xffffffff - SZ_16M);