wrappers for ->i_mutex access

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ext4/super.c

@@ -2286,10 +2286,10 @@ static void ext4_orphan_cleanup(struct super_block *sb,
 					__func__, inode->i_ino, inode->i_size);
 			jbd_debug(2, "truncating inode %lu to %lld bytes\n",
 				  inode->i_ino, inode->i_size);
-			mutex_lock(&inode->i_mutex);
+			inode_lock(inode);
 			truncate_inode_pages(inode->i_mapping, inode->i_size);
 			ext4_truncate(inode);
-			mutex_unlock(&inode->i_mutex);
+			inode_unlock(inode);
 			nr_truncates++;
 		} else {
 			if (test_opt(sb, DEBUG))