bindings: rust: update bindgen's version

bindings: rust: update bindgen's version

The currently selected version of bindgen has a unmaintained dependency
and generates the following build warning while building vhost-device
crate:

Crate:     ansi_term
Version:   0.12.1
Warning:   unmaintained
Title:     ansi_term is Unmaintained
Date:      2021-08-18
ID:        RUSTSEC-2021-0139
URL:       https://rustsec.org/advisories/RUSTSEC-2021-0139
Dependency tree:
ansi_term 0.12.1
└── clap 2.34.0
    └── bindgen 0.59.2
        └── libgpiod-sys 0.1.0
            └── libgpiod 0.1.0
                └── vhost-device-gpio 0.1.0

error: 1 denied warning found!

Fix it by moving to a later version of bindgen, which updates the types
of few of the arguments to the FFI helpers and so required changes to
few of explicit type conversions.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>