staging/lustre: Properly cast ll_fid2path argument to __user in ll_file_ioctl

When calling ll_fid2path, it expects a userspace pointer.
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/file.c

@@ -2296,7 +2296,7 @@ ll_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return 0;
 	}
 	case OBD_IOC_FID2PATH:
-		return ll_fid2path(inode, (void *)arg);
+		return ll_fid2path(inode, (void __user *)arg);
 	case LL_IOC_DATA_VERSION: {
 		struct ioc_data_version	idv;
 		int			rc;