gpio: tegra186: Remove tegra186_gpio_lock_class

This is no longer required after commit 959bc7b2
("gpio: Automatically add lockdep keys")

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>