drm/gem: Always initialize the gem object in object_init

At least drm/i915 expects that the obj->dev pointer is set even in
failure paths. Specifically when the shmem initialization fails we
call i915_gem_object_free which needs to deref obj->base.dev to get at
the slab pointer in the device private structure. And the shmem
allocation can easily fail when userspace is hitting open file limits.

Doing the structure init even when the shmem file allocation fails
prevents this Oops.

This is a regression from

commit 89c8233f
Author: David Herrmann <dh.herrmann@gmail.com>
Date:   Thu Jul 11 11:56:32 2013 +0200

    drm/gem: simplify object initialization

v2: Add regression note which Chris supplied.

Testcase: igt/gem_fd_exhaustion
Reported-and-Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
References: http://lists.freedesktop.org/archives/intel-gfx/2014-January/038433.html
Cc: stable@vger.kernel.org
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_gem.c

@@ -128,11 +128,12 @@ int drm_gem_object_init(struct drm_device *dev,
 {
 	struct file *filp;
 
+	drm_gem_private_object_init(dev, obj, size);
+
 	filp = shmem_file_setup("drm mm object", size, VM_NORESERVE);
 	if (IS_ERR(filp))
 		return PTR_ERR(filp);
 
-	drm_gem_private_object_init(dev, obj, size);
 	obj->filp = filp;
 
 	return 0;