constify vfs_truncate()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/open.c b/fs/open.c
index 17cb6b1..2f49fce 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -65,7 +65,7 @@
 	return ret;
 }
 
-long vfs_truncate(struct path *path, loff_t length)
+long vfs_truncate(const struct path *path, loff_t length)
 {
 	struct inode *inode;
 	long error;