More differentiated error codes for DRM(agp_acquire)

drivers/char/drm/drm_agpsupport.h

@@ -103,7 +103,11 @@ int DRM(agp_acquire)(struct inode *inode, struct file *filp,
 	drm_device_t	 *dev	 = priv->dev;
 	int              retcode;
 
-	if (!dev->agp || dev->agp->acquired || !drm_agp->acquire)
+	if (!dev->agp)
+		return -ENODEV;
+	if (dev->agp->acquired)
+		return -EBUSY;
+	if (!drm_agp->acquire)
 		return -EINVAL;
 	if ((retcode = drm_agp->acquire()))
 		return retcode;