drm: fix the ioctl to not believe userspace.

believing userspace causes oopses

linux-core/drm_drv.c

@@ -631,6 +631,8 @@ long drm_unlocked_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		goto err_i1;
 	}
 #endif
+	cmd = ioctl->cmd;
+
 	func = ioctl->func;
 	/* is there a local override? */
 	if ((nr == DRM_IOCTL_NR(DRM_IOCTL_DMA)) && dev->driver->dma_ioctl)