drm: Fix return value of drm_framebuffer_init()

In its original version, drm_framebuffer_init() returned a negative int
if drm_mode_object_get() failed (f453ba046074, "DRM: add mode setting
support").

This was accidentally disabled by commit 4b096ac10da0 ("drm: revamp
locking around fb creation/destruction"). Thus, drm_framebuffer_init()
pretends success if drm_mode_object_get() failed.

Reinstate the original behaviour. Also fix erroneous kernel-doc of
drm_mode_object_get().

Fixes: 4b096ac10da0 ("drm: revamp locking around fb creation/
    destruction")
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_crtc.c

@@ -306,8 +306,7 @@ static int drm_mode_object_get_reg(struct drm_device *dev,
  * reference counted modeset objects like framebuffers.
  *
  * Returns:
- * New unique (relative to other objects in @dev) integer identifier for the
- * object.
+ * Zero on success, error code on failure.
  */
 int drm_mode_object_get(struct drm_device *dev,
 			struct drm_mode_object *obj, uint32_t obj_type)
@@ -423,7 +422,7 @@ int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb,
 out:
 	mutex_unlock(&dev->mode_config.fb_lock);
 
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(drm_framebuffer_init);