udf: avoid info leak on export

For type 0x51 the udf.parent_partref member in struct fid gets copied
uninitialized to userland. Fix this by initializing it to 0.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index 1802417..c31deb3 100644
--- a/fs/udf/namei.c
+++ b/fs/udf/namei.c
@@ -1279,6 +1279,7 @@
 	*lenp = 3;
 	fid->udf.block = location.logicalBlockNum;
 	fid->udf.partref = location.partitionReferenceNum;
+	fid->udf.parent_partref = 0;
 	fid->udf.generation = inode->i_generation;
 
 	if (parent) {