Fix: lookup_fdget_rcu removed in Linux 6.13.0-rc1

Fix: lookup_fdget_rcu removed in Linux 6.13.0-rc1

See upstream commit 8fd3395ec9051a52828fcca2328cb50a69dea8ef:

    commit 8fd3395ec9051a52828fcca2328cb50a69dea8ef
    Author: Al Viro <viro@zeniv.linux.org.uk>
    Date:   Wed Jul 31 11:49:04 2024 -0400

        get rid of ...lookup...fdget_rcu() family

        Once upon a time, predecessors of those used to do file lookup
        without bumping a refcount, provided that caller held rcu_read_lock()
        across the lookup and whatever it wanted to read from the struct
        file found.  When struct file allocation switched to SLAB_TYPESAFE_BY_RCU,
        that stopped being feasible and these primitives started to bump the
        file refcount for lookup result, requiring the caller to call fput()
        afterwards.

        But that turned them pointless - e.g.
                rcu_read_lock();
                file = lookup_fdget_rcu(fd);
                rcu_read_unlock();
        is equivalent to
                file = fget_raw(fd);
        and all callers of lookup_fdget_rcu() are of that form.  Similarly,
        task_lookup_fdget_rcu() calls can be replaced with calling fget_task().
        task_lookup_next_fdget_rcu() doesn't have direct counterparts, but
        its callers would be happier if we replaced it with an analogue that
        deals with RCU internally.

        Reviewed-by: Christian Brauner <brauner@kernel.org>
        Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Change-Id: I98f1c617e8bd7ad9db7a9af2a1fa76c5eb26e8b8
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>