UBIFS: improve debugging

1. Print inode mode in some of debugging messages
2. Add few more useful assertions

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 8565e58..01598f2 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -941,7 +941,8 @@
 	struct inode *inode = dentry->d_inode;
 	struct ubifs_info *c = inode->i_sb->s_fs_info;
 
-	dbg_gen("ino %lu, ia_valid %#x", inode->i_ino, attr->ia_valid);
+	dbg_gen("ino %lu, mode %#x, ia_valid %#x",
+		inode->i_ino, inode->i_mode, attr->ia_valid);
 	err = inode_change_ok(inode, attr);
 	if (err)
 		return err;