drm/tegra: Force cast to __iomem to make sparse happy

The fbdev screen memory pointer is annotated __iomem, so cast the kernel
virtual address to that address space to make the warning go away.
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/fb.c

@@ -247,7 +247,7 @@ static int tegra_fbdev_probe(struct drm_fb_helper *helper,
 		 info->var.yoffset * fb->pitches[0];
 
 	drm->mode_config.fb_base = (resource_size_t)bo->paddr;
-	info->screen_base = bo->vaddr + offset;
+	info->screen_base = (void __iomem *)bo->vaddr + offset;
 	info->screen_size = size;
 	info->fix.smem_start = (unsigned long)(bo->paddr + offset);
 	info->fix.smem_len = size;