drm/msm: correct attempted NULL pointer dereference in debugfs

msm_gem_describe() would attempt to dereference a NULL pointer via the
address space pointer when no IOMMU is present. Correct this by adding
the appropriate check.
Signed-off-by: Brian Masney <masneyb@onstation.org>
Fixes: 575f0485 ("drm/msm: Clean up and enhance the output of the 'gem' debugfs node")
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190513234105.7531-2-masneyb@onstation.org

drivers/gpu/drm/msm/msm_gem.c

@@ -803,7 +803,8 @@ void msm_gem_describe(struct drm_gem_object *obj, struct seq_file *m)
 		seq_puts(m, "      vmas:");
 
 		list_for_each_entry(vma, &msm_obj->vmas, list)
-			seq_printf(m, " [%s: %08llx,%s,inuse=%d]", vma->aspace->name,
+			seq_printf(m, " [%s: %08llx,%s,inuse=%d]",
+				vma->aspace != NULL ? vma->aspace->name : NULL,
 				vma->iova, vma->mapped ? "mapped" : "unmapped",
 				vma->inuse);