drm: use format %d to print error code

It is more readable by printing "ret = -1" than "ret = 0xffffffff"
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_drv.c

@@ -486,7 +486,7 @@ long drm_ioctl(struct file *filp,
 		kfree(kdata);
 	atomic_dec(&dev->ioctl_count);
 	if (retcode)
-		DRM_DEBUG("ret = %x\n", retcode);
+		DRM_DEBUG("ret = %d\n", retcode);
 	return retcode;
 }