drm/gem: Don't call drm_mmap from drm_gem_mmap

The only user I could dig out was i915 back when ums+gem was still a
thing. But we've just very much killed that, and even when someone
screams about that we should resurrect that with a special hack
(wrapping drm_gem_mmap) in i915, not in the core code.

So good riddance to another entry point of the legacy buffer mapping
code.

Signed-off-by: Daniel Vetter <[e-mail]>
Reviewed-by: David Herrmann <[e-mail]>
Acked-by: Alex Deucher <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/drm_gem.c

···
 					   vma_pages(vma));
 	if (!node) {
 		mutex_unlock(&dev->struct_mutex);
-		return drm_mmap(filp, vma);
+		return -EINVAL;
 	} else if (!drm_vma_node_is_allowed(node, filp)) {
 		mutex_unlock(&dev->struct_mutex);
 		return -EACCES;