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/reiserfs/dir.c

@@ -38,11 +38,11 @@ static int reiserfs_dir_fsync(struct file *filp, loff_t start, loff_t end,
 	if (err)
 		return err;
 
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 	reiserfs_write_lock(inode->i_sb);
 	err = reiserfs_commit_for_inode(inode);
 	reiserfs_write_unlock(inode->i_sb);
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	if (err < 0)
 		return err;
 	return 0;