drm/msm: potential error pointer dereference in init()

The msm_iommu_new() returns error pointers on failure so check for that
to avoid an Oops.

Fixes: ccac7ce3 ("drm/msm: Refactor address space initialization")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20211004103806.GD25015@kiliSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c

@@ -908,6 +908,10 @@ static int _dpu_kms_mmu_init(struct dpu_kms *dpu_kms)
 		return 0;
 
 	mmu = msm_iommu_new(dpu_kms->dev->dev, domain);
+	if (IS_ERR(mmu)) {
+		iommu_domain_free(domain);
+		return PTR_ERR(mmu);
+	}
 	aspace = msm_gem_address_space_create(mmu, "dpu1",
 		0x1000, 0x100000000 - 0x1000);